Tungsten/wolfram (W) is the chemical element with atomic number 74 in group 6 of the periodic table of the elements. It is a rare metal in the earth's crust and is found in certain minerals in the form of oxides or salts.
Tungsten or wolfram is not found free in nature, but is extracted from several wolfram ores: wolframite, scheelite, ferberite, cuproscheelite, hübnerite and stolzite. The largest producers are China, Bolivia and Russia.
Tungsten is extracted from the mines in several stages: it is converted into tungsten trioxide, heated with carbon and hydrogen and powdered tungsten is produced. To obtain tungsten in its pure state, metallurgy is easy, but because it has a very high melting point, the final product is difficult to process. To achieve this, the ores are melted with sodium carbonate to produce a soluble salt comprising the tungsten. It is then treated with hydrochloric acid to produce tungsten oxide. Finally, the oxide is reduced with a hydrogen stream. This produces tungsten powder.
Properties and characteristics of tungsten
- Tungsten is a grey-coloured metal in its pure state, and is very hard and dense.
- It melts at 3,422 °C, making it the metal with the highest melting point.
- It also has the highest boiling point (5930 °C) of all known elements.
- It is the most friction resistant metal.
- It has an acceptable chemical resistance and cannot be easily attacked by acids.
- When exposed to ultraviolet light it has a very bright bluish lustre.
- Its density is 19600 kg/m3.
Types of tungsten alloys
Tungsten in its natural form is brittle and difficult to work with, but when alloyed it can be worked more easily, although it is also a difficult metal to alloy. Tungsten alloys (heavy alloys) are usually 90-97% tungsten.
- Tungsten + nickel + iron: this is the most common alloy, and it is magnetic. This alloy is perfect for radiation shielding because of its high density combined with radiation resistance.
- Tungsten + nickel + copper: these have lower ductility than the previous one. Its main advantage is that it is non-magnetic. It is used for example in oncology tools.
- Tungsten carbide (tungsten + carbon): This is not an alloy, but is a ceramic-like compound made by the sintering process in which the addition of black carbon to tungsten powder produces an extremely hard and brittle cement when cooled. It is the most important tungsten compound. It is used in industrial machinery, wear-resistant tools...
Tungsten is used to manufacture hard metal inserts and tools. Recycling of these products is very important to preserve the environment and to meet the demand for this valuable and rare material. Around 30% of tungsten scrap is recycled. Many of the recyclable materials are richer in tungsten than the ore concentrations, which is why it is so valuable to recycle these materials. The demand for tungsten products is increasing and, as a consequence, so is the demand for this resource.