Chapter_3 - Primary bonds secondary bonds Primary bonds...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Ionic Metallic Covalent Electrons: Lost Free Shared Elements: Positive+negative Metallic small diff. in electronegativity Primary bonds & secondary bonds Primary bonds Chapter 3 ME 201: Materials Science, Z. Hao 1 Orientation: Nondirectional Nondirectional Directional Secondary bonding Bonding force is much weaker than primary bonds Fluctuating dipole bonds Permanent dipole bonds Lectures are available at: Blackboard.odu.edu Æ use your midas account to log in 3.1 Three metallic crystal structures: BCC, FCC, HCP Chapter 3 Crystal Structures & Crystal Geometries Chapter 3 ME 201: Materials Science, Z. Hao 2 3.2 Cubic Unit Cells ¾ Atomic position, direction indices, and miller indices ¾ Volume, planar atomic, and linear atomic density 3.3 Polymorphism and amorphous materials A few Definitions Atoms, arranged in repetitive 3-Dimensional pattern, in long range order (LRO) give rise to a crystal solid or crystalline material . Examples: metals, alloys, and certain ceramic materials (diamond) Properties of solids depends on crystal structure and bonding force An imaginary network of lines, with atoms at intersection of lines, representing the arrangement of atoms is called space lattice . Chapter 3 ME 201: Materials Science, Z. Hao Unit cell: the block of atoms which repeats itself to form space lattice. Unit Cell Space Lattice Lattice constants a, b, c α , β , γ Types of basic unit cells Tetragonal ¾ a =b c ¾ α = β = γ = 90 0 Rhombohedral ¾ a =b = c Monoclinic ¾ a b c ¾ α = β = γ = 90 0 Triclinic ¾ a b c Seven different types of basic unit cells are necessary to create all space lattices. Table 3.1 on Page 75 Chapter 3 ME 201: Materials Science, Z. Hao Cubic Unit Cell ¾ a = b = c ¾ α = β = γ = 90 0 ¾ α = β = γ 90 0 Orthorhombic ¾ a b c ¾ α = β = γ = 90 0 a b ¾ α = β = γ = 90 0 Hexagonal ¾ a = b c ¾ α = β = γ = 90 0 Variations in basic unit cells Variations of basic unit cells Æ more atoms added in some way ¾ Simple ¾ Body Centered ¾ Face Centered ¾ Base Centered Example: Orthorhombic unit cells Chapter 3 ME 201: Materials Science, Z. Hao Simple Base Centered Face Centered Fourteen standard unit cells: describe all possible lattice networks Figure 3.2 on Page 76 Body Centered Three principal unit cells Cubic Unit Cell ¾ a = b = c ¾ α = β = γ = 90 0 Body Centered Cubic ( BCC ) Simple Cubic Chapter 3 ME 201: Materials Science, Z. Hao 6 Hexagonal ¾ a b c ¾ α = β = γ = 90 0 Simple hexagonal Face Centered Cubic ( FCC ) Hexagonal Close Packed ( HCP )
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon