Why Tungsten is so Hard: Understanding the Properties and Applications

The metal Tungsten is renowned for its extreme hardness and durability, which are attributed to its unique set of properties. Tungsten is not only one of the hardest naturally occurring metals but also exhibits exceptional heat resistance and tensile strength. In this article, we will delve into why Tungsten is so hard and explore its applications and properties.

The Properties Contributing to Tungsten's Hardness

High Melting Point: Tungsten has the highest melting point among all metals, with a melting point of 6191.6 Fahrenheit. This high melting point is primarily due to the tight mutual attraction between its atoms, which are held together by strong metallic bonds.

Densely Packed Crystals: Tungsten has a crystal structure that is densely packed, making it harder to deform. The atoms are arranged in a way that maximizes interatomic forces, resulting in greater resistance to plastic deformation.

High Density: Tungsten has a high density of 19.25 grams per cubic centimeter, which is one of the highest among metals. This elevated density means that the metal is very compact and dense, enhancing its overall hardness.

High Tensile Strength: Tungsten exhibits a high tensile strength, meaning it can withstand significant stress without breaking. This property is crucial for applications that require materials to resist high forces.

Low Coefficient of Thermal Expansion: Tungsten has a low coefficient of thermal expansion, meaning its dimensions remain relatively stable when temperatures fluctuate. This quality is beneficial in maintaining the metal's hardness under varying environmental conditions.

Tungsten's Hardness on the Mohs Scale

On the Mohs scale of mineral hardness, which ranges from 1 to 10, Tungsten is rated at around 7.5. While diamonds, the hardest naturally occurring substance, are rated at 10, Tungsten is still significantly harder than many other metals. For example, tungsten carbide, a compound of tungsten and carbon, is approximately 2 to 3 times harder than titanium and cobalt-chrome.

Comparing Tungsten to Other Hard Materials

Despite its impressive hardness, Tungsten is not the hardest material in the world. There are certain synthetic and natural materials that are even harder. For instance, wurtzite boron nitride and lonsdaleite (a form of diamond found in meteorites) both exceed Tungsten's hardness. This highlights that hardness is not just a function of density but is also influenced by intermolecular and intramolecular forces.

The Chemistry and Physics Behind Hardness

Hardness is a measure of a material's resistance to localized plastic deformation. It depends on the inter-molecular and intra-molecular forces within the material. In Tungsten, the strong metallic bonds and tightly packed crystal structure contribute to its hardness. The interatomic forces are extremely strong, making it difficult to force the atoms apart. Additionally, the high density of Tungsten means there are more atoms in a given volume, further contributing to its hardness and strength.

Applications of Tungsten

Given its extreme hardness and durability, Tungsten is used in a wide range of applications, including:

High-temperature Applications: Due to its high melting point, Tungsten is used in electrodes for electric lamps and heating elements.

Ballistic Applications: Due to its extreme hardness, Tungsten is used in armor and bulletproof vests.

Industrial Tools: Tungsten carbide is used in cutting tools and machine parts due to its hardness and resistance to wear.

Metallurgy: Tungsten is used as a hardener in alloy steels and in the production of special-purpose metals.

In conclusion, Tungsten's hardness is a result of its unique properties, including its high melting point, dense crystal structure, and strong interatomic bonds. Its hardness makes it a valuable and versatile material with numerous applications across various industries.