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問題一覧
1
What are the fundamentals of atomic bonding?
After bonding, atoms need to be neutrally charged and have filled outer shells, Metal atoms lose electrons, Non-metal atoms gain electrons
2
What is a metal?
A material that loses electrons during bonding
3
What are the types of bonding?
Ionic - an atom gaining an electron from another atom that needs to lose an outer shell electron, Covalent - two atoms sharing outer shell electrons, becoming stable in the process, Metallic - many atoms release their outer shell electrons into an "electron cloud", individual atoms are charged but whole system is stable
4
What is meant by directional interatomic bonds?
Bonds between atoms where electrons are typically found in specific regions, as opposed to being evenly distributed (non-directional bonds)
5
Which characteristics of materials change with stronger bonds?
The temperature required to melt the material rises, The material becomes stiffer
6
What are some examples of materials that have covalent, ionic, and metallic bonds?
Covalent - Diamond, carbon fibre, Ionic - Ceramics (e.g. alumina - aluminium oxide, Al(2)O(3), Metallic - Metals (e.g. copper)
7
What about metallic bonds gives metals their common characteristics?
Electrons are free to move within the metal - makes them conductive and appear shiny, Bonding is non-directional - Makes them ductile
8
Which property of a material can be significantly changed by alloying and/or heat treatment?
Yield strength
9
What is a lattice and a unit cell?
Unit Cell - Smallest unit of atoms that can be used to produce a lattice, Lattice - A regular repeated arrangement of unit cells
10
What is a crystal?
A 3-dimensional material with a regular repeated arrangement of atoms in a lattice structure
11
What is a hexagonal close packed structure?
A structure where close packed groups of atoms are layered in an ABA pattern - the third layer is added directly above the bottom plane
12
What is a face centered cubic structure?
A structure where close packed groups of atoms are layered in an ABC pattern - the third layer covers the gaps left by the first 2 layers
13
How do layers in a body centered cubic differ from the other structures and what is the reason for this?
Despite being metallic bonds, there is a slight directivity of bonds, so the planes only have 2 close packed directions as opposed to 3
14
What is a body centered cubic structure?
A structure where nearly close packed groups of atoms are layered in an ABA pattern - the third layer is added directly above the bottom plane
15
What is the packing factor?
A measure of how closely packed atoms are, which also determines density, = Volume of all Atoms in Unit Cell / Total Volume of Unit Cell
16
What are the packing factors of each structure?
Hexagonal Close Packed = 0.74, Face Centered Cubic = 0.74, Body Centered Cubic = 0.68
17
What are slip systems?
Total number of directions in which slip can easily occur - in crystals, these involve close (or nearly close) packed planes
18
What are slip directions?
The number of directions in which slip planes can be moved
19
What is the formula for the number of slip systems?
Slip Systems = Slip Planes × Slip Directions per Plane
20
Which characteristics do metals with many slip systems have?
High ductility and a lower yield stress
21
How many slip systems do the unit cells for the 3 metallic structures have?
Hexagonal Close Packed - 3 (one slip plane with 3 close packed directions), Face Centered Cubic - 12 (4 slip planes with 3 close packed directions), Body Centered Cubic - 12 (6 slip planes with 2 close packed directions)
22
Why aren't the slip systems for a body centered cubic the same as a face centered cubic, despite having the same amount of slip systems, and what are the consequences of this?
Because the planes aren't perfectly close packed (only close packed in 2 directions rather than 3), It is slightly harder to slide layers over each other, making them stronger, The plastic behaviour of body centered cubics varies with temperature, meaning they can become more brittle at low temperatures and more ductile at high temperatures
23
What are examples of metals with a hexagonal close packed, face centered cubic, and a body centered cubic structure?
Titanium, Copper, gold, aluminium, Iron, tungsten, chromium