Graphite Flashcards
What are the three types of graphite?
Flake, compacted, and spheroidal
Which type of graphite is most brittle, and why?
Flake; has long, thin graphite flakes with sharp notches at the ends which act as stress raisers
Which type of graphite is weakest, and why?
Flake; application of load is almost wholly supported by matrix (of pearlite), yet is a small % of total structure due to least distance between the flakes
Which type of graphite is strongest, and why?
Spheroidal; distance between spheres is greater and so matrix is a larger % of total structure. Load is almost wholly supported by matrix
Which type of graphite is most ductile, and why?
Spheroidal; spheres are best shapes for avoiding stress raisers
What is the structural composition of spheres in spheroidal graphite?
Are long thin plates wrapped around each other and which nucleate from a point; appears spherical but is comprised of cones
What is compacted graphite?
Intermediate of flake and spheroidal; has large distance between flakes and spheres so is stronger than flake graphite, but has flakes present so is more brittle` than spheroidal
Why was spheroidal graphite iron created in China so much earlier than in Western civilisation?
Chinese iron ores were very pure, producing facetted eutectic graphite spheres in the iron; western iron ores contained S and P, acting as modifiers which formed unfacetted flake grpahite instead
How can modifiers increase properties of Al-Si alloys?
Addition of Na produce non-facetted eutectic Si (fibre like instead of flake-like), preventing growth along ledges and doubling mechanical properties
In 1943, what modifier was added to cast iron?
Mg; created nearly perfect spheres of graphite, allowing ductility
In 1948, what modifier was added to grey iron?
Cerium; produced spherical graphite in hypereutectic grey iron
How is aluminium extracted?
Electrolytic reduction of alumina (Al2O3)
What are common Al alloys?
Al-Si, Al-Cu
