Materials

Properties of solid materials

The properties of solid materials are defined by the strength of the atoms or molecules that keep them together. In the case of solids, we can distinguish between chemical and physical properties. Some of the physical properties are also known as bulk properties (see below).

Physical properties of solid materials

The physical properties of solid materials can be intensive or extensive, and their classification depends on how the property reacts to an increase in mass.

If a mass increase modifies the property, it is an extensive property. If an increase in mass does not affect the physical property, it is an intensive property. See the following list of extensive and intensive properties:

Extensive properties :

• Mass, measured in kg.
• Volume, measured in cubic units.
• Length, measured in metres.

Intensive properties :

• Density, measured in mass over volume.
• Temperature, measured in degrees (Celsius, Fahrenheit, Rankine, or Kelvin).
• Conductivity, measured in Siemens per length of material.
• Malleability, measured in pressure units.

Material colours

An extraordinary property of materials is their colours, which are caused by the reflection of light when the electromagnetic waves in the visible spectrum (light as you know it) impact an object. The way an object’s atoms or molecules are arranged also affects a material’s colour.

The property of the colour of materials is used by areas of science that study light reflected by objects to understand which elements are responsible for the composition of objects.

What is a bulk property in a solid?

Solids exhibit properties, such as density, elasticity, conductivity, etc., which determine how the atoms in the solid work together as a ‘bulk’. The bulk properties are directly related to the solid’s composition and how its atoms are bound together. These bulk properties are important in engineering applications, as they can tell us how the solid works and what forces it can withstand. Some bulk properties are listed below:

• Density, measured in kg / m ^ 3.
• Conductivity, measured in S / m ^ 3, where S is Siemens.
• Elasticity, measured in Pascals (Pa).
• Hardness, measured in Pascals.

Density

Density is described as a material’s mass per unit of volume. The volume in solids depends on how tightly packed their particles are. The elements that make up the solid can affect this, as in the following two examples:

Conductivity

Conductivity defines how easily a material conducts electricity. It describes how the atom’s electrons and its structure work together to move electrical charges from one place to another.

Elasticity

Elasticity is the property that tells us how easy it is to deform an object. Elastic objects deform when very little strength is applied. Examples of elastic materials include rubber and metals. Any object or material that does not deform easily is named ‘inelastic’.

Hardness

Hardness is the property that defines how strongly a material resists deformation over a small area, as, for instance, when you push the lead of a pencil into an object and the object offers resistance against the lead. A material’s hardness is related to how the atoms or substances of which it is composed are bonded together. For example, a diamond’s atoms are strongly bonded together, which makes it a hard material.

How do we measure bulk properties?

A material’s bulk properties are measured using mechanical tests. During each test, materials are exposed to forces that seek to deform, penetrate, or compress them. The experiments measure the force values against the deformations made in the object.

Every bulk property can be measured using mechanical tests. Some of these are listed below:

• Conductivity test: passing an electrical current through a material.
• Elasticity test: deforming a material by pulling it or compressing it.
• Hardness test: pushing a sharp, hard object against the material and increasing the force used to push that object.