Tungsten(W): Properties, Use, Health & Environmental Effects

Overview

Tungsten also referred to as wolfram is a chemical element with the symbol W and atomic number 74. Natural tungsten contains five stable isotopes and 21 other unstable isotopes. The name Tungsten comes from the former Swedish name for the tungstate mineral scheelite, tungsten which means heavy stone. Pure tungsten is a silver-white metal which is solid at room temperature and when made into a fine powder can be combustible and can spontaneously ignite.

Tungsten is very strong and durable and thus it can be useful in very many different ways. It is very resistant to corrosion and has the highest melting point and highest tensile strength of any element. It is only slightly attacked by most minerals acids. Its strength comes when it is made into compounds, though pure tungsten is very soft.

What You Need To Know About Tungsten

Discovery

In 1779 Irish chemist Peter Woulfe discovered the existence of a new element, Tungsten from his careful examination of the mineral Wolframite (an iron manganese tungstate mineral) from Sweden.

Tungstate was later isolated as tungstic oxide (WO₃) in 1781 in Sweden by Wilhelm Scheele from the mineral Scheelite (calcium tungstate). However, he did not have a suitable furnace to reduce the oxide to the metal.

Tungsten was finally isolated by brothers Fausto and Juan Jose de Elhuyar in 1783 in Spain. They produced the same acidic metal oxide (tungstic oxide -WO₃) and even reduced it to tungsten metal by heating it with carbon.

Occurrence In Nature 

Tungsten is a rare metal found naturally on Earth almost exclusively combined with other elements in chemical compounds rather than alone. Its most common ores are the minerals Scheelite or calcium tungstate (CaWO₄) and wolframite or iron manganese tungstate (Fe,MnWO₄). The abudance of tungstate in the Earth’s crust is thought to be about 1.5 parts per million.

Periodic Table Facts

The periodic table is a chart that shows how chemical elements are related to one another. Metals in the same group have very similar physical and chemical properties.

• The atomic symbol of tungsten is W.
• In the periodic table, tungsten is located in group 6 , period 6, d-block. 
• Tungsten is categorized as a transition metal in the periodic table.
• The atomic number of cobalt is 74. Atomic number is the number of protons.
• The ground state electronic configuration of neutral tungsten is [Xe]4f¹⁴5d⁴6s²
• Electrons per shell in tungsten are 2, 8, 18, 32, 12, 2.

Physical Properties

• Pure tungsten is a light gray or whitish metal that is soft enough to be cut with a hacksaw and ductile enough to be drawn into wire or extruded into various shapes.  
• Tungsten is more resistant to fracturing than diamond and is much harder than steel.
• Tungsten is a solid at standard temperature and pressure.
• Tungsten has the highest melting point and lowest vapor pressure of all metals. The melting point of tungsten is 3695K (6192^oF, 3422^oC).
• Boiling point of Tungsten is 5930^oC (6203K, 10706^oF).
• Density of tungsten at standard temperature and pressure is 19.3 grams per cubic centimeter (g/cm³).
• The heat of fusion of tungsten is 52.31 kJ/mol.
• The heat of vaporization of tungsten is 774 kJ/mol.
• Tungsten has a Molar heat capacity of 24.27 kJ/mol.
• The enthalpy of fusion of tungsten is 35 kj/mol.

Other Properties

• Tungsten does not occur as a free metal. It is primarily extracted from two types of minerals, that is, wolframite (an iron manganese tungstate) and scheelite (calcium tungstate, CaWO₃).
• Tungsten has excellent corrosion resistance and is attacked only slightly by most mineral acids.
• Commercially, tungsten is obtained by reducing tungsten oxide with hydrogen or carbon.
• Tungsten has electrical resistivity of 52.8 nΩ.m (at 20^oC).
• Thermal conductivity of tungsten is 173.72 W/(m.k).
• Tungsten is paramagnetic at standard pressure and temperature.
• The naturally occurring tungsten consists of five isotopes, four are considered stable (¹⁸²W, ¹⁸³W, ¹⁸⁴W and ¹⁸⁶W) whereas one is considered slightly radioactive (¹⁸⁰W).
• Tungsten forms binary compounds with halogens (known as halides), oxygen (known as oxides), and hydrogen (known as hydrides).
• The atomic weight of tungsten is 183.85. Atomic weight is the average mass of the atom.
• The electronegativity of tungsten according to pauling scale is 1.7
• The first and second Ionization energies of tungsten is 770 kJ/mol and 1700 kJ/mol respectively.
• The Van der  waals radius of tungsten is 0.137nm.
• Tungsten has a body-centered cubic crystal structure.
• The atomic radius of tungsten is 139 pm.

Reaction

Reaction With Acids

Tungsten metal is largely unaffected by most acids.

Reaction with water

At room temperature, tungsten does not react with water.

Reaction With Bases

Tungsten metal does not react to any significant extent with dilute solutions of hydroxide.

Reaction with Halogens

Tungsten reacts with fluorine at room temperature to form tungsten (VI) fluoride.

W(s) + 3F₂(g)―>WF₆(s)

Tungsten reacts directly with chlorine Cl₂ at 250^oC or bromine Br₂ to form tungsten (V) chloride and tungsten (V) bromide respectively.

W (s)+ 3Cl₂(g)―> WCl6(s) [dark blue]

W(s) + 3Br₂ (l)―> WBr6(s) [dark blue]

2W(s) + 5Cl₂ (g) ―> 2WCl₅(s) [dark green]

Extraction

Tungsten is primarily extracted from two types of minerals ores, scheelite and wolframite. The metal is obtained commercially by reducing tungsten oxide with hydrogen or carbon. Powdered tungsten (VI) oxide is heated to temperatures in the range of 550-850^oC in a stream of hydrogen.

Pure metallic tungsten cannot be obtained by reducing tungsten VI oxide using carbon because it reacts with carbon to make tungsten carbide. Instead, the reducing agent is hydrogen.

However, tungsten recycling also accounts for about 35% of the global supply. China is the world’s largest producer of the metal, providing over 75% of the world supply.

Uses Of Tungsten (W)

• Tungsten forms compounds with calcium and magnesium that have phosphorescent properties and are used in fluorescent light bulbs.
• Tungsten-steel alloys are used to make high speed cutting tools and rocket engine nozzles.
• Tungsten carbide (WC or W₂C) is extremely hard and is used to make drills. It is also used for jewelry because of its hardness and wear resistance.
• Compounds of tungsten such as tungsten disulfide is used a dry lubricant in temperatures as high as 932 degrees Fahrenheit (500^oC).
• Tungsten’s heat resistance makes it useful in arc welding applications when combined with another highly-conducive metal such as silver or copper.
• Due to its strength at high temperatures, tungsten is used in many high-temperature applications such as cathode-ray tube, vacuum tube filaments, heating elements and rocket nozzles.
• In electronics, tungsten is used as an interconnect material in integrated circuits between silicon dioxide dielectric material and the transistors.
• Tungsten powder is used as a filler material in plastic composites which are used as a nontoxic substitute for lead in bullets, shot and radiation shields.
• The density of tungsten is similar to that of gold, thus, tungsten can be used in jewelry as an alternative to gold or platinum.
• High-density alloys of tungsten with nickel, copper or iron are used in high-quality darts.
• Tungsten is also used as a target for X-ray production.
• Tungsten salts are used in the chemical and tanning industries.
• Tungsten is used in fabrication of spacecraft and missile parts.

Health & Environmental Effects

• Scientists have shown that soil exposure to tungsten at rates higher than 1% can stunt the growth of plants, cause reproductive problems in earthworms and trigger premature death in certain aquatic animals. It also induces the death of red worms and plants.
• Tungsten has no know chronic effect in human beings, however repeated or prolonged occupational exposure to tungsten is known to affect the eyes, skin, respiratory system and blood or can aggravate medical conditions.

Summary Of Properties Of Tungsten In Tabular Form