Вольфрам(VI) оксид

Химические свойства

Canary-yellow, heavy powder, darkorange when heated and regains original color on cooling. Insoluble in water, soluble in caustic alkalies, soluble with difficulty in acids. Noncombustible.

Физические свойства

Heavy yellow powder; turns dark orange on heating; reverts back to yellow on cooling; density 7.2 g/cm³; melts at 1,472°C; insoluble in water; slightly soluble in acids; soluble in caustic alkalies.

Использование

manufacture of tungstates which are used for x-ray screens and for fireproofing fabrics.

Подготовка

Tungsten trioxide is obtained as an intermediate in recovery of tungsten from its minerals (See Tungsten). In commerical processes tungstic acid, H2WO4, obtained from the mineral scheelite, may either be decomposed at high temperatures to form trioxide or dissolved in ammonium hydroxide solution and evaporated to yield ammonium paratungstate (APT) crystals, 5 (NH₄)₂O?12WO₃?11H₂O. The APT crystals are then washed, dried, and calcined at elevated temperatures to form tungsten trioxide
Tungsten trioxide, in general, can be made by heating metallic tungsten, its carbides, its lower oxides, or tungstic acid in air.

Общее описание

Tungsten(VI) oxide (WO₃) is a semiconducting material with excellent electrochromic properties. It is a cost efficient material with a high optical modulation. It can be synthesized by a variety of methods which include chemical vapor deposition, electrodeposition, and other sol-gel based coating processes.

Опасность

Toxic material.

Профиль безопасности

Moderately toxic by ingestion. Can react violently with ClF3, Li, Cl2. See also TUNGSTEN COMPOUNDS.

Структура и конформация

The crystal structure of tungsten trioxide is temperature dependent. It is tetragonal at temperatures above 740℃, orthorhombic from 330 to 740 °C, monoclinic from 17 to 330 °C, triclinic from -50 to 17 °C, and monoclinic again at temperatures below -50 °C.The most common structure of WO3 is monoclinic with space group P21/n.