Introduction material
- 1. MATERIALS SCIENCE AND ENGINEERING An Introduction Naman Kumar Gandhi Mechanical Engineering Indore institute of technology & Science Naman.gandhi@indoreinstitute.com
- 2. Introduction to Material science and Engineering • Atomic structure in Materials • Atomic Bonding in Materials • Types of material • Crystal structure of materials • Crystalline solids and their role in influencing various properties
- 3. What is an atom? • Atom: the smallest unit of matter that retains the identity of the substance. • Consists of a central nucleus surrounded by one or more electrons WHAT IS THE NUCLEUS • The central part of an atom. • Composed of protons and neutrons. • Contains most of an atom's mass.
- 4. Atomic Structure • Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus • Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well
- 5. WHAT IS AN ELECTRON? oNegatively charged particle. oLocated in shells that surround an atom's nucleus.
- 6. WHAT IS A NEUTRON? o Uncharged particle. oFound within an atomic nucleus.
- 7. WHAT IS A PROTON? oPositively charged particle. oFound within an atomic nucleus.
- 8. Atomic Structure • Atoms are composed of 2 regions: – Nucleus: the center of the atom that contains the mass of the atom – Electron cloud: region that surrounds the nucleus that contains most of the space in the atom
- 9. Particle Charge Mass (g) Mass (amu) Proton +1 1.6727 x 10-24 g 1.007316 Neutron 0 1.6750 x 10-24 g 1.008701 Electron -1 9.110 x 10-28 g 0.000549
- 11. Bonding in Materials • Primary Bonding There are three types of primary bonds 1. Ionic Bonding 2. Covalent Bonding 3. Metal Bonding
- 12. Ionic Bonding • Ionic bonding occurs between charged particles. Ionic bonding occurs between metal atoms and nonmetal atoms. • Metals usually have 1, 2, or 3 electrons in their outermost shell. Nonmetals have 5, 6, or 7 electrons in their outer shell. Atoms with outer shells that are only partially filled are unstable. To become stable, the metal atom wants to get rid of one or more electrons in its outer shell. Losing electrons will either result in an empty outer shell or get it closer to having an empty outer shell. It would like to have an empty outer shell because the next lower energy shell is a stable shell with eight electrons.
- 13. Some Common Features of Materials with Ionic Bonds: • Strong and high energy bonds • High melting point • Non directional • Hard and brittle or cleave rather than deform Transparent • Insulator
- 14. Covalent Bonding • Where a compound only contains nonmetal atoms, a covalent bond is formed by atoms sharing two or more electrons. Nonmetals have 4 or more electrons in their outer shells (except boron). With this many electrons in the outer shell, it would require more energy to remove the electrons than would be gained by making new bonds. Therefore, both the atoms involved share a pair of electrons. Each atom gives one of its outer electrons to the electron pair, which then spends some time with each atom. Consequently, both atoms are held near each other since both atoms have a share in the electrons.
- 15. Some Common Features of Materials with Covalent Bonds: 1. Often hard 2. Inorganic covalent compounds usually have high melting point 3. Can be strong (Diamond) 4. Can be weak (Bi) 5. Directional
- 16. Metallic Bonding The outermost electron (valance electron) of metal atoms are weakly bound and when such atoms interact to become a solid, their valence electrons form a “gas of electrons known as electron gas. Thus metallic bond results from the attraction between the positive metal ions and the electron gas. The electron gas acts to hold the positive metal ions to form metallic bond which provides the high electric and thermal conductivitities and other characteristic properties of metals.
- 17. Some Common Features of Materials with Metallic Bonds • Good electrical and thermal conductors due to their free valence electrons • Opaque • Relatively ductile • High packing density • Metallic bonds are weaker than ionic and covalent bonds. • They are crystalline in nature.
- 18. Secondary Bonding Van der Waals Bond The van der Waal bonds occur to some extent in all materials but are particularly important in plastics and polymers. These materials are made up of a long string molecules consisting of carbon atoms covalently bonded with other atoms, such as hydrogen, nitrogen, oxygen, fluorine. The covalent bonds within the molecules are very strong and rupture only under extreme conditions. The bonds between the molecules that allow sliding and rupture to occur are called van der Waal forces.
- 19. Hydrogen Bonds • Thus when water molecules are close together, their positive and negative regions are attracted to the oppositely-charged regions of nearby molecules. The force of attraction, shown here as a dotted line, is called a hydrogen bond. Each water molecule is hydrogen bonded to four others.
- 20. Types of material 1. Metals 2. Ceramics 3. Polymers 4. Composites 5. Semiconductors 6. Bio Materials
- 21. Metals & Alloys • Mechanical behavior of metals and alloys • Tensile & compressive stress-strain relations • Fracture toughness, fatigue, creep, wear and abrasion • Microstructure properties and applications of ferrous and non-ferrous alloys • Alloys
- 22. Atomic arrangement in Solids • Crystalline – periodic arrangement of atoms: definite repetitive pattern • Non-crystalline or Amorphous – Random arrangement of atoms.
- 23. Structure of Crystalline Solids • Face Centered • Body Centered • Hexagonal closed crystal structure
- 24. Crystallography Structure and Geometry of crystals • Space lattice A space lattice is an infinite array of points in three-dimensional Space in which each point is identically located with respect to the other. It is a periodic arrangement of points arranged in regular manner and having repeat distance in three directions which are termed as fundamental lattice vectors. At these lattice positions we place atom, or group of two, three etc. atoms we obtain a crystalline solid. The crystal structure is real while the lattice is imaginary
- 25. Unit Cell the smallest group of atoms which has the overall symmetry of a crystal, and from which the entire lattice can be built up by repetition in three dimensions. Types of units cells • A units cell is obtained by joining the lattice points. The choice of lattice points to draw a unit cell is made on the basis of the external geometry of the crystal, and symmetry of the lattice. There are four different types of unit cells. These are, • (1) Primitive or simple cubic(sc) : Atoms are arranged only at the corners of the unit cell. • (2) Body centered cubic (bcc) : Atoms are arranged at the corners and at the center of the unit cell. • (3) Face centered cubic(fcc) : Atoms are arranged at the corners and at the center of each faces of the unit cell. • Lattice points are the positions where you can place an atom. If there are two lattice point in a unit cell it means two atom will stay in single unit cell
- 26. 3 • tend to be densely packed. • have several reasons for dense packing: -Typically, only one element is present, so all atomic radii are the same. • have the simplest crystal structures. 74 elements have the simplest crystal structures – BCC, FCC and HCP We will look at three such structures... METALLIC CRYSTALS
- 27. 4 • Rare due to poor packing (only Po has this structure) • Close-packed directions are cube edges. • Coordination # = 6 (# nearest neighbors) (Courtesy P.M. Anderson) SIMPLE CUBIC STRUCTURE (SC) Click on image to animate
- 28. 5 • APF for a simple cubic structure = 0.52 Adapted from Fig. 3.19, Callister 6e. ATOMIC PACKING FACTOR
- 29. • Coordination # = 8 8 Adapted from Fig. 3.2, Callister 6e. (Courtesy P.M. Anderson) • Close packed directions are cube diagonals. --Note: All atoms are identical; the center atom is shaded differently only for ease of viewing. BODY CENTERED CUBIC STRUCTURE (BCC) Click on image to animate
- 30. a R 9 • APF for a body-centered cubic structure = 0.68 Unit cell c ontains: 1 + 8 x 1/8 = 2 atoms/unit cell Adapted from Fig. 3.2, Callister 6e. ATOMIC PACKING FACTOR: BCC
- 31. 6 • Coordination # = 12 Adapted from Fig. 3.1(a), Callister 6e. (Courtesy P.M. Anderson) • Close packed directions are face diagonals. --Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing. FACE CENTERED CUBIC STRUCTURE (FCC) Click on image to animate
- 32. Unit cell c ontains: 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell a 7 • APF for a body-centered cubic structure = 0.74 Adapted from Fig. 3.1(a), Callister 6e. ATOMIC PACKING FACTOR: FCC
- 33. 10 • Coordination # = 12 • ABAB... Stacking Sequence • APF = 0.74 • 3D Projection • 2D Projection A sites B sites A sites Adapted from Fig. 3.3, Callister 6e. HEXAGONAL CLOSE-PACKED STRUCTURE (HCP)
- 35. fcc
- 38. • Atoms may assemble into crystalline or amorphous structures. • We can predict the density of a material, provided we know the atomic weight, atomic radius, and crystal geometry (e.g., FCC, BCC, HCP). • Material properties generally vary with single crystal orientation (i.e., they are anisotropic), but properties are generally non-directional (i.e., they are isotropic) in polycrystals with randomly oriented grains. 27 SUMMARY