Mats Lecture 6 Flashcards
Crystal Structure of Metal
What is the definition of Crystalline?
A material where the atoms are perfectly spaced at uniform distance from each other
-A crystalline material has long range atomic order
What families of materials are almost always crystalline?
-Almost all metals (only a few are amorphous)
-All ceramics
What is the definition of Non-Crystalline or Amorphous?
-A material where the atoms are not uniformly spaced
-No long range atomic order
What families of materials are Amorphous?
-Most glasses (Quartz: crystalline SiSO2)
-Most polymers are amorphous or semi-crystalline (some can be 100% crystalline)
What is the definition of lattice?
-Is a collection of points (lattice points), a regular repeated 3 dimensional arrangement of atoms, ion or molecules in a metal or other crystalline solid
What is the definition of unit cell?
-The smallest portion of a crystal lattice
-The simplest repeated unit in a crystal structure
-The entire lattice is made up of repeated unit cells in different directions
How many unique ways can you arrange points in 3D?
14 (the fourteen Bravais lattices)
What are the 14 Bravais lattices grouped into? List them
-7 Crystal System:
-Cubic
-Tetragonal
-Orthohombic
-Trigonal
-Hexagonal
-Monoclinic
-triclinic
What is a coordination number?
-Number of nearest neighbouring atoms for a particular atom
-It is an indiction of how tightly and efficiently packed the atoms are
What is the definition of a close packed direction?
-Direction through which the atoms are touching in the unit cell
What is the Atom Packing Factor (APF) of a BCC (Body-Centred Cubic)?
What does the number give you?
(Volume of atoms in the unit cell)/volume of the unit cell
-How much of the crystal is made up of atoms
-If the number is subtracted from 100, it gives you how much the structure is made up of nothing
What are some abbreviations of close-packed atomic stacking?
-CPH
-FCC
What is a solid known as if it’s formed by the stacking of close packed layers of atoms in the ABABABAB… sequence?
-Hexagonal close packed (HCP) or called Close Packed Hexagonal (CPH)
What is a solid known as if it’s formed by the stacking of close packed layers of atoms in the ABCABCABC… sequence?
-Face Centered Cubic (FCC)
How many atoms are contained in HCP Unit cell?
6 atoms
