T6 Flashcards
Why does material degrade when you recycle it?
More impurities are added like paints and coatings
Why are carbon fibre composites hard to recycle?
Hard to separate fibre from matrix phase. Where this is possible, the fibres are crushed which shortens fibre length. This means the fibres aren’t continuous and aligned so mechanical properties decrease.
4 ways galvanic corrosion can be prevented:
1) coupling of dissimilar metals, pick two that are close on the galvanic scale
2) avoid unfavourable anode/cathode ratio, want big anode area
3) electrically insulate dissimilar metals from each other
4) electrically connect a third anodic metal to the other two (cathodic protection)
How to prevent crevice corrosion?
Weld joins instead of using bolts or rivets. Remove accumulated deposits frequently and design containment vessels that avoid stagnant areas and drain well.
What happens in swelling and dissolution of polymeric materials?
The solute molecules diffuse to and occupy positions among the polymer macromolecules and force them apart
How does cross linking and crystallinity decrease swelling and dissolution?
Greater intermolecular bonding between adjacent chains which restricts the number of solute molecules that can fit into the locations.
Cross linking is better since crystalline bonds are secondary ones (VDW) and are weaker than covalent (crosslinks)
Difference in corrosion of metals and ceramics:
1) ceramics are more resistant to corrosion
2) ceramic corrosion is normally chemical dissolution but metals it’s electrochemical
3) ceramics more resistant at higher temps
Difference in corrosion in metals and degradation of polymers:
1) polymer degradation is physiochemical but metals it’s electrochemical
2) degradation mechanisms of polymers are more complex than metal corrosion
3) more types of degradations for polymers e.g. dissolution, swelling and bond rupture
Why does adding chromium to stainless steel make it corrosion resistant?
It forms a tough, adherent, corrosion resistant oxide surface layer. It doesn’t flake of like iron oxide (rust)
What are inhibitors?
Substances that when added to a corrosive environment decrease the places corrosiveness. E.g. eliminate a chemically active species from a solution, attach inhibitor molecules to corroding surface to interfere with OILRIG, formation on thin protective coating on corroding surface.
Difference between brittle and ductile fracture:
Ductile materials exhibits lots of plastic deformation with high energy absorption before failure whereas there’s little/no deformation/energy absorption with brittle fractures.
