Introduction To Tungsten And Tungsten Crucibles

1. What is Tungsten?

Tungsten is a chemical element extracted from its ores, namely wolframite and scheelite. It was identified as a new element in 1781 and isolated in 1783. It exhibits the highest melting point among metals, high tensile strength, high density and low vapour pressure. Its atomic number is 74 and it is denoted by the symbol W. The name tungsten originates from the Swedish term "Tung sten", meaning heavy stone.

2. Occurrence of Tungsten

Tungsten Metal occurs naturally in the minerals wolframite, ferrite, scheelite and hubnerite. China produces most of the tungsten, while Russia, Canada and Bolivia supply the remainder.

To extract tungsten from its ores, they are crushed, purified and treated with alkaline solutions to yield tungsten trioxide. Thereafter, tungsten trioxide is heated with carbon or hydrogen gas, resulting in tungsten metal with carbon dioxide or water vapour.

3. Principal Applications of Tungsten

A. Alloys

Tungsten is used in the production of cemented carbide alloys because of its hardness and density. Its high melting point qualifies it for manufacturing rocket nozzles, turbine blades and wear‐resistant components. Tungsten alloys are employed in the automotive and aerospace sectors.

B. Tungsten Carbide

Tungsten carbide (WC) is a significant product that forms a part of cemented carbides. It is widely utilised in modern tools for precision applications.

C. Electronics

Tungsten is used in the manufacture of various electronic devices, including incandescent light bulbs, cathode ray tubes, vacuum tubes, heating elements and electrical contacts. Other devices incorporating tungsten include field emission apparatus, electron microscopes and transistors.

D. Gold Replacement

Tungsten has a density comparable to that of gold. Consequently, it is used as a substitute in the manufacture of jewellery and in the production of resistors that resist scratching and forgery.

4. Introduction to Tungsten Crucibles

Tungsten crucibles are containers made from tungsten or tungsten alloys. They are used for melting and calcining materials at high temperatures. They are manufactured in various designs and shapes to meet specific customer requirements. Tungsten crucibles are often produced with up to 0.9% molybdenum or with trace amounts of other elements. Given that detailed specifications are provided, the following uses are noted:

- They are primarily used for the growth of sapphire and single crystals. They are also used for melting rare earth metals.
- Owing to their resistance to certain metal oxides and molten metals, tungsten crucibles are utilised in the manufacture of electronic components and in thermal evaporation methods.
- They are also used in heating elements for induction furnaces, in metal melting processes and in the fabrication of high-temperature containers.