Tungsten trioxide powder may be used as a near infrared shielding material with long working life, which is mainly determined by its photochromic properties. Photochromism refers to the reversible change of a substance between two physical or chemical states, at least, one of which is caused by light radiation. The changing process can be expressed by the following equation:
The basic characteristics of changing process of photochromism process is shown as bellow:
(1) T1 and T2 can be stable under certain conditions;
(2) The color parallax of T1, T2 is significantly different;
(3) The changing process between T1 and T2 is reversible.
Since tungsten trioxide has these excellent properties, it can also be used in display materials, sensors, and decorative materials, etc. By hydrothermal method, using sodium tungstate and hydrochloric acid as raw materials, hexagonal tungsten trioxide photochromic powder can be synthesized under the conditions of pH=1.0, T=120°C. And the obtained powder may be applied in buildings or automobiles for saving energy.
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