Wolframoxid

Wolframoxid, also known as tungsten(VI) oxide, is the inorganic compound with the chemical formula WO3. It is a stable, non-volatile solid at room temperature and occurs as a pale yellow to white powder. The compound has a high melting point (about 1473 °C) and a wide band gap, and in its pure form it is a poor conductor of electricity. WO3 can exist in several polymorphs depending on temperature, and it may exhibit blue coloration when reduced to tungsten bronzes.

Occurrence and production

In nature, tungsten is found primarily in the minerals scheelite (CaWO4) and wolframite ((Fe,Mn)WO4). Industrial production of WO3 is achieved by oxidizing tungsten-bearing concentrates or metal at elevated temperatures to convert tungsten to tungsten(VI) oxide, followed by purification steps. WO3 can also be prepared by oxidation of elemental tungsten or by processing tungsten compounds from ore concentrates.

Properties

WO3 is chemically stable in air and reacts with strong reducing agents. It forms various intercalation compounds, including blue tungsten bronzes, upon introduction of alkali metals. The material is used as a precursor for many tungsten compounds and serves as a versatile oxide with catalytic and electrochemical relevance.

Applications

Wolframoxid serves as a catalyst in oxidation and dehydrogenation reactions and as a material for electrochromic coatings in smart windows, where it changes color upon ion intercalation. It is also employed in gas sensing and as a pigment in ceramics and glass. As a solid oxide, it is a key starting point for producing tungsten carbide and other tungsten-containing materials.

Safety

Dust or powder forms can be irritating if inhaled; handling should follow standard inorganic oxide safety practices, including proper ventilation and protective equipment. WO3 is relatively insoluble in water.