Choosing the correct material for any particular task is essential for a manufacturing
activity. Materials are divided into: Raw materials (natural and artificial) and
processed materials (artificial materials).
Natural materials exist in nature, and we use them as they are. Examples of these
materials are wood, stone, sand, wool, etc. Natural resources are split into 3 categories:
animal, vegetable and mineral. In technical works, most of the materials are mineral and
often also vegetable as in the case of wood. Every natural material has to be modified
for future use. For instance, wood has to be dried in order to remove the moisture. The
element iron has to be removed from the iron oxide mineral in a mineral oven and so
Thus, iron oxide or wood from a tree are raw materials that have to be converted
into elemental iron and wood pieces, which become processed materials.
Processed materials can be obtained from other processed materials too. For example,
iron is used to get steel and steel is used to obtain stainless steel. But in all these objects,
where are the artificial objects? An artificial object is the one that has been created by
Properties of Materials
Properties of materials can be divided mainly into physical and chemical properties. It’s
very important to define every property, including what the physical state (solid, liquid
or gas) of a material is. There exists a fourth state that is not very common, called
plasmatic state or plasma. All the properties defined in this lesson cannot be applied to
Extension activity: Find out further information about plasma, what its appearance is,
where it can be found, what differences exist between plasma and the other physical
Density refers to the relation between the mass and volume of a solid. Density is
measured in Kg/m3, according to ISO units.
Dilation, contraction and Fusibility
Dilation: When material expands ( get bigger)due to heat
Contraction: When material shrinks or contracts (gets smaller) due to heat
Fusibility is the ability of a material to change into a liquid when heated to its melting
point. Examples of melting points
Iron melting point is 1535
Copper melting points 8083
Strength refers to the resistance of a solid to being bent, broken or having its form and
dimensions modified. To test the strength of a solid, try to deform it. Strength can be
studied under several conditions, such as the following: Compressive strength, tensile
strength, Torque or torsion and Flexure or Bending. According to the degree of
deformation, solids can be split into those with plastic deformation and those with
elastic deformation. In the first case, the strength is enough to make a permanent
deformation. Elastic deformed solids, however, return to their original forms at the
moment the forces being exerted are over.
Ductility is the ability of solid materials to be drawn out into wires. It typically occurs
in soft metals like copper, aluminum and tin.
Malleability is the ability of solid materials to be flattened into boards and plates.
Usually, ductility and malleability are properties found in the same kinds of materials.
Thermal and Electrical Conductivity: Both are the ability of heat or electricity to run
through the material, respectively. In both cases, the materials can be good conductors
or bad conductors. In the latter case, the material is called an insulator. Examples:
Copper is a good electrical and thermal conductor but polyethylene or Teflon is used as
Optical properties describe how materials behave when light touches them. They can be
a) Opaque: No light travels through them. e.g wood
b) Transparent: All light travels through them, and you can see what’s behind the
materials. e.g a glass window pane
c) Translucent: All light can travel through them but you cannot see what’s behind
them e.g frosted glass
These properties refer to the ability of materials to conduct sound. Sound is a sort of
mechanical vibration, and vibration in a material produces transient elastic
deformations. The behavior of a material in conducting sound depends on whether it’s
solid, liquid or gas because collisions between molecules are how sound is transmitted.
Activity to think about: Could you speak on the moon?
Oxidation: The change that occurs to most metals when in contact with oxygen
from air or water. Sometimes the oxidation becomes corrosion.
Recyclability: Materials that can be reused to make new ones by chemical
separation of their components are recyclable. Sometimes those materials that
are separated to be reused are simply used as fuel.
Toxicity: Materials which are harmful to the environment
Biodegradability: Materials that decompose naturally with time are
biodegradable. For example, an apple takes about 20 days to decompose, plastic
takes about 100 years, and glass takes about 400 years.