Metals

Question 1

State the 3 most common metallic structures

Answer 1

• body centred cubic
• hexagonal close packed
• face centred cubic (cubic close packed)

Question 2

Summarise polymorphism

Answer 2

• metals can change their structure as a function of temperature and pressure
• seperate from state: the crystal structure is changing!

Question 3

How would we prove a metal’s structure? & an equation commonly used in the process?

Answer 3

• x ray diffraction

- bragg’s law nλ=2dsinθ

Question 4

Summarise solid solution

Answer 4

• a solid “mixture” like a solution in the way that there’s different proportions of different components

Question 5

Summarise substitutional solid solutions

Answer 5

• random replacements of atoms in a particular structure
• crystal structures are normally the same
• sizes of the atoms must be similar (circa 15%)
• Must have similar redox properties to avoid electron transfer (when e transfer occurs get intermetallics)
  eg brass (Cu/Zn) bronze (Cu/Sn)

Question 6

Summarise interstitial solid solutions

Answer 6

• insetion of atoms into small gaps in structure
• interstitial is typically small
• may be random or regularly distributed
• eg steel (Fe/C)

Question 7

Summarise intermetallics

Answer 7

• significant difference in electronegativity results in e- transfer
• has regular crystal structure
• typically interesting M-M bonding
  eg K4Si4, maraging steel, memory metal

Question 8

Define grain

Answer 8

• small crystaline region in a metal

Question 9

Summarise annealing

Answer 9

• material heated to just below softening point in order to adjust its internal structure

Question 10

How do normal and shear stress operate

Answer 10

• normal stress through the axis of a material (perpen. to its cross section) thus UNIAXIAL (one direction)
• shear stress perpen to the axis of a material (takes place in a plane)

Question 11

Summarise dislocations

Answer 11

• line defects

- they can propagate through metals allowing them to slip past each other