Materials Science at a Glance Atomic Structure Sina Askarinejad 1/1 3/25/2016

Materials Science and Engineering Fundamental Structures Crystallography Bonding Properties Processing 1mm Atomic structure (Angstrom) [1] Nano-structure (1-10 nm) Macrostructure (1mm- meter) Micro-structure (100 nm-1 mm) [1] A. Navrotsky (1998). "Energetics and Crystal Chemical Systematics among Ilmenite, Lithium Niobate, and Perovskite Structures". Chem. Mater. 10(10): 2787. doi:10.1021/cm9801901.

Materials in Industry Metals: Hard, opaque, shiny, good thermal and electrical conductivity, heavy. Ceramics: Inorganic crystalline material, compounded of a metal and a non-metal. Stiff, brittle, usually not conductive (there are semiconductors and superconductors), light, high-temperature resistance Glass: A non-crystalline ceramic. Transparent, brittle, highly resistant to chemical attack, light. Polymers: Large molecules or macromolecules, composed of many repeated subunits. Low strength, low stiffness. Composites: A material made of two or more constituent materials with very different properties.

Askeland, D. R. , & Phulé, P. P. (2003) Askeland, D. R., & Phulé, P. P. (2003). The science and engineering of materials.

Atomic Structure of Materials Structure of atoms: Electrons (9.11 e-28 gr) Protons and Neutrons (1.67 e-24 gr each) Avogadro number: 6.022 e23 (The number of atoms or molecules in 1 mole) 1 mole of carbon= 1 mole of (6 protons + 6 Neutrons)= 12gr

Orbitals and Energy Levels Shell Sub-shell K L M N P

Electronegativity: The tendency of atoms to absorb electron.

Atomic Bonding Metallic Bonds Covalent Bonds Ionic Bonds Van der Waals

Metallic bonds

Covalent

Ionic Bond Different atoms

Van der Waals Induced dipole & Induced dipole London forces Debye interaction Induced dipole & Permanent dipole Keesom Interaction Permanent dipole & Permanent dipole

Hydrogen bond is a special type of Keesom interaction Hydrogen bond is a special type of Keesom interaction. It is between hydrogen and N or O or F. Van der Waals forces are responsible for physical properties of materials such as melting point, glass transition temperature and surface tension. high melting point and surface tension of water is due to the hydrogen bonding.

Mixed Bonding Usually, the bond between atoms is a mix of different atomic bonds. Bonds between Iron atoms are a mixture of metallic and covalent bonding. Bonds between two metallic atoms is intermetallic bond which is a mixture of metallic and ionic bond.

Structure and mechanical properties

Carbon! One of the most interesting materials in nature Has allotropes: Diamond Graphite Buckyballs Carbon nanotubes

Diamond Each atom has 4 covalent bonds. One of the highest melting point materials known: 3550 °C. One of the highest know thermal conductivity: 2000 W/mk. Stiffest material in the world: 1100 GPa. Electrical insulator. One of the hardest materials in the world. So it is used in cutting tools.

Graphite Three covalent bonds and one van der Waals. High melting point due to the strong covalent bonds. Lower density than diamond. It is electrically conductive due to the one free electron.

Buckyballs (C60) Each carbon has two single bonds and one double bond. Extremely strong and superconductive.

Carbon Nanotubes (CNT) Rolled version of a single layer graphite (graphene). Reinforcement in polymers. Electrically Conductive.

Short-range and long-range order

Lattice structures

When materials can have more than one crystal structure: For pure materials: Allotropy (Iron, titanium) For compound materials: Polymorphism (Silica, Zirconia)

Diffraction Techniques When a beam of x-ray with same magnitude and wavelength, strikes a crystal, it scatter in all directions. Most of these scattered waves will cancel others, however, in specific angles for specific crystallographic structures, they reinforce each other. This is called diffraction. Bragg’s law: