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Unformatted text preview: 1 Phase Diagrams A phase diagram shows what phases are present at a given temperature, pressure, and composition Phase = part of material having uniform structure and composition, can be solid, liquid or gas Application story: rocket nozzle cone 2 Phase Diagram for Graphite/ Diamond Pressure Temperature 14 kBar 1000 K 34 kBar Graphite Diamond 300K 1 Bar = 10 5 Pa " 1 atm 3 Making Diamond at Low Pressures 1% methane + 99% hydrogen Electric (plasma) discharge at 10-1- 10-3 Torr Substrate at 800 - 1000 C Simultaneous deposition of graphite and diamond Atomic hydrogen in the gas discharge etches graphite faster than diamond, resulting in net deposition of diamond 4 NaCl+H 2 O: a common binary system Pure H 2 O ! 21 o C % NaCl 23.3% NaCl Temperature ( o C) Liquid (brine) Salt + brine Ice + brine Ice + salt O-10-20 10 10 20 30 NaCl has negligible solubility in ice 5 Cooling Curve for Pure Cu Time Temperature 1085 C 6 Cooling Curve for Cu 50 Ni 50 Temperature Time 1260 C 1320 C 7 Phase Diagram for Ni+Cu Temperature ( C) % Ni 1085 1453 Pure Cu Pure Ni Solidus Liquidus LIQUID (L) SOLID ( # ) # +L 1 2 A B C 1 C 2 (binary isomorphous system) 8 Lever Rule Temperature Pure A Pure B LIQUID (L) SOLID ( # ) # +L w L w o w # T 9 Lever Rule L # w L w o w # X L = w " # w o w " # w L X " = w o # w L w " # w L 10 Pb+Sn: binary eutectic system Pb Sn C1 C2 C4 C3 327 C 232 C 183 C # $ $ +L # +L L # + $ 18.318....
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