Material Science Fundamentals: Bonds, Structures, and Properties
Chemical Bonds
A chemical bond is the force responsible for the stable union between ions, atoms, or molecules, forming substances.
Ionic Bond
Occurs between elements with very different electron affinity. It is common in substances formed by a metal (which yields electrons) and a nonmetal (which captures electrons).
Covalent Bond
Arises between atoms of the same or similar elements. It is common among nonmetals.
Metallic Bond
Usually occurs between metallic elements, as they have delocalized electrons in their outer layer, forming an “electron sea.”
Metallic Lattices
Body-Centered Cubic (BCC)
The atoms occupy the center and the corners of a cube.
Face-Centered Cubic (FCC)
The atoms occupy the vertices and the center of the cube faces.
Hexagonal Close-Packed (HCP)
The atoms occupy the vertices and the center of the bases of the prism.
Classification of Materials
Natural Materials
Materials that already exist in nature.
Artificial Materials
Materials obtained from natural sources through processing.
Synthetic Materials
Materials made from artificial processes, often from simpler chemical precursors.
Ceramic Materials
Have low electrical and thermal conductivity, are used as insulators, and are hard but brittle.
Metallic Materials
Possess characteristic brightness, good electrical and thermal conductivity, high strength, ductility, and malleability. They are useful in structural or load-bearing applications.
Plastic Materials
Composed of long molecular chains (polymers) obtained from simple molecules (monomers). They have low conductivity and low strength but good toughness.
Composite Materials
Formed from two or more materials from different groups, combining their properties for various applications.
Advanced Materials
Materials that have been modified in structural or chemical form for use in applications where unmodified materials were not suitable. These include nanotechnology, new biomaterials, and others.
Physical Properties
Extensivity
The capacity of a body to occupy a three-dimensional space and possess volume.
Impenetrability
The resistance of a body to be penetrated or pierced by another, preventing it from occupying the same space.
Density
The relationship between the mass of a certain amount of material and the volume it occupies.
Specific Volume
The inverse of density.
Specific Gravity
The relationship between the weight of a quantity of material and the volume it occupies.
Resistivity
The resistance offered to the passage of current by a material element 1m long and 1m2 in cross-section.
Electrical Conductivity
The ability of a material to allow the passage of electric current through it. Materials can be:
- Conductors: Have low resistivity.
- Insulators: Have very low conductivity.
- Dielectrics: Are good insulators and are used to improve the effectiveness of capacitors.
- Semiconductors: Exhibit intermediate electrical behavior; at low temperatures, they are insulators, and at high temperatures, they are conductors.
- Superconductors: Very good conductors of electric current that do not lose energy as heat.
Mechanical Properties
Cohesion
The strength of molecules to resist separation.
Hardness
The resistance a body offers to being penetrated by another.
Elasticity
The ability to recover the original shape when the deforming force ceases.
Plastic Deformation
The ability to acquire permanent deformation without fracturing.
Ductility
The ability to plastically deform under tensile stress and be drawn into wires.
Malleability
The ability to plastically deform under compressive stress and be hammered into sheets.
Toughness
The ability to absorb energy from sudden external impacts without fracturing.
Brittleness
Lack of resistance to sudden shocks, leading to fracture with little plastic deformation.
Fatigue
The resistance to fracture under repetitive stress of varying magnitude.
Resilience
The ability to absorb energy in the elastic zone without permanent deformation, and release it upon unloading.
Chemical Properties
Oxidation (Dry and Warm)
A chemical reaction in which an element loses electrons to an oxidizing component.
Corrosion (Humid Atmosphere)
The slow, progressive destruction of a material caused by oxygen and moisture. It can be:
- Uniform Corrosion: The affected area’s thickness is equal across the metal surface, leading to a uniform decrease in the piece’s thickness and mechanical strength.
- Localized Corrosion: Produces pits, holes, and grooves on the surface, concentrating damage in specific areas.