Understanding Metals and Plastics: Properties & Processes
Metals
Metals are usually obtained from the transformation of minerals, which are rocks extracted directly from nature.
Some metals, such as gold, silver, platinum, and copper, can be found in their purest form and are called native metals.
Physical Properties
Electrical conductivity is the property that allows the passage of electrical current.
Thermal conductivity is the property of materials to transmit heat.
Density is the amount of material mass per unit volume.
Expansion is the relative variation of a material’s dimensions due to temperature change.
The melting point is the temperature at which a material changes from a solid to a liquid state.
Fusibility is the property of a material that refers to the amount of heat needed to melt it.
Types of Stress
Traction is the stress on a piece caused by two opposing forces that pull.
Compression is the stress on a piece caused by two opposing forces that crush it.
Flexion is the stress on a piece caused by forces tending to bend it.
Shear is the stress on a piece caused by two opposing forces exerted on different but very close points, tending to cut the piece.
Twist is the stress on a piece caused by two forces that tend to twist it, deforming it around an axis.
Response to Stress
Elasticity is the property of deformed materials to return to their initial shape when the stress is removed.
Plasticity is the property of materials to retain deformations caused by stress after the stress is removed.
Malleability is the property of materials to permanently deform when subjected to compression.
Ductility is the property of materials to permanently deform when subjected to traction.
Other Mechanical Properties
Hardness is the property of materials to resist being scratched or penetrated.
Toughness is the resistance to breakage that a material exhibits when hit.
Fatigue is the resistance to breakage that a material exhibits when subjected to repeated stress.
Machinability is the property that refers to the ease with which a material can be machined or worked.
Weldability is the property of some materials to join together solidly by the effect of heat, sometimes with additional materials.
Important Chemical Reactions
Oxidation is the reaction of a material with oxygen in the environment.
Corrosion is the process of material deterioration due to chemical reactions with substances in the environment.
Biological Properties
Recyclability is the property that refers to our ability to transform a used product into a new product.
Biodegradability is the property of materials to deteriorate as a result of interactions with the environment.
Toxicity is the property of materials that have negative effects on organisms.
Plastics
1. Obtaining Raw Materials
Raw materials may be of mineral, plant, or animal origin.
2. Synthesis of Monomers
While in some cases monomers are obtained directly from nature, a chemical process is usually necessary for extraction of raw materials.
3. Synthesis of the Polymer Core
Raw materials undergo various chemical processes, including polymerization.
4. Incorporation of Additives
Specific substances are added to polymers to give them specific properties.
5. Forming and Finishing
The resulting product from the previous stages is worked to give it its final form.
Obtaining Raw Materials
- Animal
- Vegetable
- Mineral Source
Additives
Dyes and Pigments add color.
Plasticizers enhance plasticity and intensify the brightness of surfaces.
Antistatic agents reduce electrostatic charges, preventing dust and dirt from adhering.
Flame retardants delay the formation of flames.
UV Stabilizers protect against ultraviolet radiation (UV) and atmospheric phenomena, also preventing decomposition.
Loads, reinforcements, and lubricants improve mechanical properties and enhance the manufacturing process.
Release agents