Density of Metals

Density of Metals

Density is vital when choosing the suitable metal material for specific applications. It is one of the primary physical properties engineers will consider when selecting the right material for the job, especially if the application is weight-related.

• What is Density?

Density is the relationship between the mass of metal and the space taken by that metal (size). Density measures how heavy a metal size is in reference to the mass of the material per unit volume.

Most metals have a uniform structure. Their atoms are regularly packed together in a crystal structure. This means these materials have a well-defined density which will have a minimal difference in different samples of the same material.

• Factors Affecting Density

Density measures the ratio of the mass of a substance to its volume. The calculated density is unique to that substance. Although the density is constant in different samples of the same metal, some factors can cause differences in density.

• Size

The first factor that will change the density of a metal is its size. The density depends on size and mass. The size is variable, so the density will also vary because their relationship is inversely proportional. If the metal has a smaller volume, it will have greater density, although the mass will remain constant.

• Pressure

As the particles of metals get closer to each other, the density increases. Pressure can bring particles closer to each other, reducing the size of the metal and increasing density. The higher the pressure on metal, the greater the density.

• Heat

Heat causes the particles of metal to move and separate from each other increasing volume. The volume is inversely proportional to the density and uniform with heat, and the heat is inversely proportional to the density.

However, the atoms in metals are closely packed and don't move far from each other when subjected to heat. Therefore, the change in density among metals is usually minimal. 

Why is The Density of Metals Important?

Density plays a critical role in selecting metal materials for various applications. Some of the reasons why metals density is highly considered in the selection process include;

• Materials interaction

In applications that require multiple types of metal, it's imperative to determine how the metals will interact with each other and the environment around them. An important consideration here is making floating devices like boats and ships. The density of the selected metal is critical because water is less dense.

• Determining the weight

Weight is a critical factor in design, especially in transport applications. Lightweight transport devices play a crucial role in reducing cars' environmental impact and running costs and increasing aircraft payload. Weight also plays a vital role in making racing cycles, among other weight-sensitive applications.

In some cases, high density and, therefore, weight are desirable properties like making weights for scales, bullets, hammers, coins and shells.

• Determine stiffness

While minimising weight, most applications still require that you make a stiff or strong component. Therefore, density is often considered alongside Young's modulus or strength to determine specific stiffness of specific strengths to determine the best metals for various applications.

• How to Calculate Density

The formula for calculating density is dividing the mass (m) of the metal by its volume (V). The formula therefore is;

ρ = m / V

Mass has the SI unit of kilogram (KG), and volume has the SI unit of a cubic meter (m3). Hence density will have the SI unit of kg/m3.

Although density is not the sole focus of the metals selection process, it has a critical role, particularly in weight-related applications.