Materials Science: Classification and Connections

Materials Science Introduction

• Jonathan Ive considers learning about materials absolutely essential for a designer.

Materials Classification

• The main classes are metals, ceramics, polymers (organic), and composites. This classification is based on their chemical makeup and atomic structure.
• Metals and non-metals are two overarching classifications of materials.
• A materials classification tree proceeds from broad categories (Metals/Non-Metals, Inorganic/Organic) to increasingly specific subcategories like Native Metals, Synthetic/Engineered Metals, Ceramics, Polymers, and Small Molecular Materials (Organic).

Connection to Other Fields

• Materials science and engineering are connected to physics, solid-state physics, crystallography, mineralogy, chemistry, bio-chemistry, bio- and environmental sciences.
• It also connects to engineering design, chemical engineering and processing, mechanical/electrical/civil engineering, and architecture/product design.

Engineering Material Menu

• Engineering materials can be broadly categorized in the following:
• Metals (Steels, Cast irons, Aluminum alloys)
• Ceramics (Aluminas, Silicon carbides, Silicon nitrides)
• Glasses (Soda glass, Borosilicate glass, Silica glass)
• Polymers (PE, PP, PET, PC, PS, PEEK, PA (nylons), Polyesters, Phenolics, Epoxies)
• Elastomers (Isoprene, Neoprene, Butyl rubber, Natural rubber, Silicones, EVA)
• Hybrids (Composites, Sandwiches, Segmented structures, lattices, foams)

Functional Materials Classification

• Functional classifications include:
• Structural materials (Steel, aluminum alloys, concrete, glass fiber, plastics, woods)
• Biomedical materials (Hidroxiapatite, titanium alloys, stainless steels)
• Electronic materials (Si, GaAs, Ge, BaTiO3, conductive polymers, Al, Cu, W)
• Magnetic materials (Fe, Fe-Si, NiZn y ferrites)
• Intelligent materials (PZT, shape memory alloys, MR fluids, aerogels)
• Materials related to energy and environment (UO2, Ni-Cd, ZrO2, LiCoO2)

Levels of Order in Materials

• Macrostructure refers to features visible without magnification, eg NaCl crystals.
• Microstructure refers to features visible with a microscope eg grain boundaries in crystalline structures
• Atomic arrangement refers to the arrangement of atoms and molecules in a center cubic structure

Bravais Lattices

• A lattice describes the arrangement of atoms, ions, or molecules in a crystalline solid.
• There are 14 different Bravais lattices that describe all possible crystal structures.
• The simplest are Cubic Simple, Cubic Body Centered and Cubic Face Centered lattices.
• Others include: Tetragonal, Orthorhombic, Monoclinic, Hexagonal, Triclinic, and Rhombohedral.

Interatomic Bonding

• Material properties depend on interatomic bonding.
• The main types of bonding are ionic, covalent, metallic, and Van der Waals (secondary) forces.

Ionic Bonding

• Found in compounds of metallic and nonmetallic elements.
• Metallic atoms give up valence electrons to nonmetallic atoms, forming ions.
• Characterized as nondirectional, where bond magnitude is equal in all directions.
• Ionic materials are typically terrible electrical conductors, hard, and stiff.
• Classic ionic material: Sodium chloride (NaCl).

Covalent Bonding

• Covalent bonds are formed by sharing electrons between adjacent atoms.
• Covalent bonds are directional, which means it limits ductility and have high fusion points
• Covalent bonds are typical in polymers and many ceramics.
• Materials with covalent bonds are bad electrical conductors, have low ductility, but high stiffness

Metallic Bonding

• Metallic materials have one, two, or three valence electrons
• Valence electrons are not bound to particular atoms and can drift throughout the metal.
• Metallic bonds are nondirectional.
• Metals are good electrical conductors at low temperatures and are ductile.

Secondary (Van der Waals) Bonding

• Physical bonds are weak compared to primary or chemical bonds.
• Groups of molecules are joined by these bond types.
• Molecules can be constituted by covalent or ionic bonds.

Material Properties and Bonding Type

• Physical and mechanical properties depend on the bonding type.
• Metals are electrical and heat conductors, deformable, and tough.
• Ceramics are good insulators, non-deformable, resistant to high temperatures, and brittle.
• Polymers are flexible, deformable, and cannot resist high temperatures.

Material/Bonding Chart:

• Metals: Metallic bonding.
• Polymers: Covalent and Secondary bonding.
• Ceramics: Ionic and Covalent bonding.