Materials And Properties

THE MATERIALS AND THEIR PROPERTIES

Raw materials
Substances directly extracted from nature.
According to their origin we can classify them into three groups:
- Animal: raw materials coming from animals. Examples: wool, silk, fur.
- Plant: raw materials deriving from plants. Examples: timber, cork, cotton, linen.
- Mineral. Examples: clay, sand, marble, iron minerals.

Material
Anyprepared matter which is ready to use in order to construct objects.
Examples: timber, plastics, metals, glass, stone, ceramics, textiles.

Technological product
Any object, tool, etc. created by humans to satisfy their needs and improve their quality of life.

- We obtain RAW MATERIALS from nature
- Raw materials are transformed into MATERIALS
- Materials are used to make TECHNOLOGICALPRODUCTS.

PROPERTIES

Characteristics that make a material behave in a certain way upon external stimuli such as light, heat, forces, environment, presence of other materials, etc.
They can be classified into:
- Physical properties
- Chemical properties
- Environmental properties

PHYSICAL PROPERTIES

These properties can be noticed upon stimuli such as electricity, light, heat andforces.

ELECTRICAL PROPERTIES
They are those that determine the behaviour of the material when an electrical current is passing through it.

- Electrical conductivity
Ability of a material to conduct electrical energy.
Depending on this ability we can distinguish:
- Conductors: materials which conduct electricity. Examples: metals, water.
- Insulators: they do not conduct or they doit at a minimum extent. Examples: plastics, paper, timber.
- Semi-conductors: they can act as a conductive or as an insulating material depending on a variety of conditions such as pressure, temperature or light. They are used in many electronic components such as transistors, diodes or integrated circuits.
OPTICAL PROPERTIES

These properties can be seen when the material is exposed to light.Depending on the behaviour of the materials we can classify them into:

- Opaque: they do not allow the light to pass through.
- Transparent: they allow almost all the light to pass through them so that we can clearly see the objects behind them.
- Translucent: they allow the passage of some of the light so that we can see the objects through them but not clearly.

Another opticalproperty is colour: it corresponds to the colour of the light that the surface of the material reflects.

THERMAL PROPERTIES

They can be seen when the material is exposed to heat.

- Thermal conductivity.
Ability of the materials to transmit heat. The materials that easily transmit heat are thermal conductors (such as metals) and those that do not easily transmit heat are called thermalinsulators (such as timber and plastics)

- Thermal expansion
It consists of an increase of the size of a material when heated. All the materials show this property, but in the case of metals, it is more noticeable. Alternatively when a material is cooled, it normally contracts.

- Fusibility
Ability of a solid material to pass into a liquid state by raising its temperature to its melting point.Metals, stones, ceramics, a few textiles, and some plastics can fuse. On the contrary, timber and a few plastics and textiles cannot fuse when heated because they burn.

MECHANICAL PROPERTIES

They describe the behaviour of a material when submitted to the action of external forces. Let´s study some of them:

- Elasticity
Ability of an object to change its shape when submitted to externalforces recovering its shape when those forces cease.

- Plasticity
Ability of an object to change its form under external forces not recovering its initial shape when ceasing those forces.
In practice, most of the materials have some elastic and some plastic properties as they can recover their initial shape but not completely. Many materials (such as metals) are elastic up to a limit and...