Optical grade yellow tungsten oxide can be produced by sol-gel method.
Sol-gel method adopts ammonium paratungstate (APT) as precursor, adding in ethyl and esters in a certain ratio. After reaction, tungstic acid sol is obtained. After a period of aging process, tungstic acid sol is converted into tungstic acid gel, and then by drying, calcinating tungstic acid to obtain yellow tungsten oxide powder (YTO).
Sol-gel method, SG method for short, is a kind of mild producing method of materials. Yellow tungsten oxide with smaller grain size can be prepared by this method. But this method costs high so that it is suitable for experiment or research institution instead of industrial production.
Principle of Sol-gel Method
Convert metal oxides or concentrated solutions of hydroxide into gel. Dry and calcinate the gel to obtain the corresponding oxide.
Sol-gel method uses inorganic material or metal alkoxide as precursor. Mix these raw materials in liquid phase, with hydrolysis reaction and condensation reaction. It will form stable transparent gel system in the solution. After aging, gel particles agglomerated gradually and form three-dimensional space structure gel.
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