Understanding Material Properties and Classes

Types of Materials

Materials are substances whose properties make them useful for the fabrication of structures, machinery, and other products.

Material Classification Groups

Materials are typically classified into groups:

• Metals and Alloys (e.g., iron, steel, aluminum)
• Polymers (e.g., nylon, polyurethane)
• Ceramics and Glass (e.g., alumina, magnesia)
• Composite Materials (e.g., wood, cermets)

Material Properties

Key material properties include:

• Chemical Properties
• Physical Properties
• Mechanical Properties
• Aesthetic and Economic Properties
• Fabrication Properties

Chemical Properties

Chemical properties include behavior related to oxidation and corrosion.

Oxidation

Oxidation occurs when a material combines with oxygen, forming oxides.

Corrosion

Corrosion is a form of oxidation that occurs in a wet environment or in the presence of other aggressive substances.

Physical Properties

Physical properties include:

• Density and Specific Gravity
• Electrical Properties
• Thermal Properties
• Magnetic Properties
• Optical Properties

Density and Specific Gravity

Density is the relationship between the mass of a certain quantity of material and the volume it occupies. The inverse magnitude of density is called specific volume.

Specific gravity is the ratio of the density of a material to the density of a reference substance (usually water).

Electrical Properties

All substances exhibit some resistance to electrical current flow. This property, which depends on the material's nature, is called resistivity.

Based on resistivity, materials are classified as conductors or insulators, depending on whether they permit the passage of electrical current. Semiconductors also exist.

Thermal Properties

Thermal properties are those related to temperature, including:

• Thermal Dilatation: Its origin lies in the fact that with increasing temperature, the vibrations of the particles increase, leading to a greater separation between them.
• Specific Heat: The amount of heat energy required to raise the temperature of a unit mass of the substance by one degree without phase changes occurring.
• Melting Temperature: When heating a solid, dilatation occurs, but if heating continues, a point is reached where the magnitude of vibration is such that the material structure cannot be maintained, and melting occurs.
• Diffusion: The thermal motion of atoms in a solid can cause displacement of atoms from its equilibrium position to other positions.

Mechanical Properties

Aesthetic and Economic Properties

Fabrication Properties