Things to remeber for exams - specific cases

Question 1

what to watch for in diamond structure

Answer 1

• CCP/FCC based but not fully because the close packed direction is on [111] NOT on [110] i.e. body diagonal NOT face diagonal
• this is not obvious because there are not atoms all the way across the body diagonal so atomic separation (centre to centre) is 1/4 [111] or 1/4 sqrt(3) a
• also inversion centre is not where expected, it’s at (1/8,1/8,1/8)
• there are more diagonal mirror planes than expected

Question 2

what structure does glass generally have, why would heat treated glass act differently

Answer 2

• generally glass is non-crystalline, isotropic and non-birefringent
• heat treated glass may become crystalline especially near the edges as this would be the first site of nucleation (heterogeneous)
• Hence certain regions at the edges of heat treated glass may be birefringent

Question 3

what is a useful equation in determining the magnitude of our burgers vector

Answer 3

FOR bcc and fcc:

b = mod(~b~) = a/2 sqrt(u^2 +v^2 + w^2)
where
a/2 [UVW] is our burgers vector

Question 4

what does the cooling curve for a hypo (or hyper) -eutectic composition look like

Answer 4

• initially linear negative
• change of gradient, still linear negative as entering L+α region
• then horizontal section where liquid undergoes eutectic transformation
• then decreasing again

Question 5

when calculating microstructure proportions for a eutectic alloy (even if cooled to room temperature), what temperature should we calculate it for

Answer 5

• the eutectic temperature