浙江大学材料热力学与动力学.ppt
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1、Chapter 1 : Thermodynamics and Phase Diagrams,1-1,Chapter 1 : Thermodynamics and Phase Diagrams,1-2,1.0.1 Thermodynamics Systems,Chapter 1 : Thermodynamics and Phase Diagrams,1-3,Open System can exchange mass, heat and work with its surroundings Closed System no mass exchange, heat and work exchange
2、 possible Isolated System no mass, no heat, no work exchange,Chapter 1 : Thermodynamics and Phase Diagrams,1-4,A. Energy, Heat and Work,The energy of an isolated system is constant The work done on a thermally isolated system is independent of the type of work and the route,1.0.2 The First Law of Th
3、ermodynamics,Chapter 1 : Thermodynamics and Phase Diagrams,1-5,Chapter 1 : Thermodynamics and Phase Diagrams,1-6,Chapter 1 : Thermodynamics and Phase Diagrams,1-7,Chapter 1 : Thermodynamics and Phase Diagrams,1-8,Chapter 1 : Thermodynamics and Phase Diagrams,1-9,1.0.3 The Second Law of Thermodynamic
4、s,Chapter 1 : Thermodynamics and Phase Diagrams,1-10,Chapter 1 : Thermodynamics and Phase Diagrams,1-11,2 parts of DS (inner and external),DSinner : from inner processes DSexner : due to heat exchange,DSexter,reversible process : DS i = 0, DS = DS e irreversible process : DS i 0, DS DS e adiabatic p
5、rocess : DS e = 0, DS = DS i irr. adiabatic process : DS 0 rev. adiabatic process : DS = 0,Chapter 1 : Thermodynamics and Phase Diagrams,1-12,The Second Law of Thermodynamics,The entropy of a closed system can not decrease.,Clausius: Heat can not flow automatically from cold side to hot side.,perpet
6、ual machines,type I,Planck: Such a process is impossible if its only result were to exchange heat to work.,type II,Chapter 1 : Thermodynamics and Phase Diagrams,1-13,Mr. Tompkins in Paperback G. Gamow Cambridge University Press, 1965,Heat can not flow automatically from cold side to hot side !,Chapt
7、er 1 : Thermodynamics and Phase Diagrams,1-14,1.1 Equilibrium in a Closed System,Chapter 1 : Thermodynamics and Phase Diagrams,1-15,How is system stability measured ? by its Gibbs free energy (at const. T and P),G = H - TS,(1.1),H : a measure of the heat content of the system ( H = U + PV ) S : a me
8、asure of the randomness of the system,low T : TS small, solids are most stable (strongest atomic binding, low H) high T : TS dominates, liquids or gases are stable (atoms more free, high S),Chapter 1 : Thermodynamics and Phase Diagrams,1-16,Stable, Metastable and Unstable,G,dG = 0,B,A,C,dG = 0,dG =
9、0,an arbitrary state parameter,B,A,C,Stable: graphite, single crystal silicon,Metastable: diamond, amorphous,Unstable: super-cooling liquid (nucleation),B,A,C,Chapter 1 : Thermodynamics and Phase Diagrams,1-17,Possibility and Realizability : Thermodynamics and Kinetics,G,B,A,C,G1,G2,Energy Hump,DG =
10、 G2 G1 0 : only possible for the transformation from B to A Amorphous Alloy (short-lived), Diamond (long-lived) Temperature : kinetic key (vibration frequency and amplitude),Chapter 1 : Thermodynamics and Phase Diagrams,1-18,Chapter 1 : Thermodynamics and Phase Diagrams,1-19,1.2 Single Component Sys
11、tems,Chapter 1 : Thermodynamics and Phase Diagrams,1-20,Chapter 1 : Thermodynamics and Phase Diagrams,1-21,Chapter 1 : Thermodynamics and Phase Diagrams,1-22,Hsolid,Hliquid,Gsolid,Gliquid,T (K),H, G,298,at all temperature: H liquid H solid since G = H - TS G liquid G solid at low T G liquid G solid
12、at high T,Tm,DHm,at Tm : H liquid - H solid = DHm G liquid = G solid,solid stable,liquid stable,H,G,Chapter 1 : Thermodynamics and Phase Diagrams,1-23,Chapter 1 : Thermodynamics and Phase Diagrams,1-24,Tm,T,DG,G,GS,GL,Free energies,at Tm,1.2.3 The Driving Force for Solidification,G L = H L - TS L,G
13、S = H S - TS S,DG = DH - TDS = 0,for most metals L R (8.3 J mol-1K-1),at T with small DT , ( Tm - T = DT ),can be ignored, DH & DS independent on T,difference on,Chapter 1 : Thermodynamics and Phase Diagrams,1-25,1.3 Binary Solutions,1.3.1 The Gibbs Free Energy of Binary Solutions,XA mole A,XB mole
14、B,XA + XB = 1,MIX,1 mole A+B,G1 = GAXA + GBXB,G2 = G1 + DGmix,DGmix : mixing free energy,DGmix = DHmix - TDSmix,Chapter 1 : Thermodynamics and Phase Diagrams,1-26,1.3.2 Ideal Solutions,DHmix = 0 DSmix = -R ( XAlnXA + XBlnXB ) DGmix = RT ( XAlnXA + XBlnXB ),Note: Since XA and XB are 1, DSmix is posit
15、ive, DGmix is negative.,XB,0,1,Molar free energy G,GA,GB,G 0,DGmix,At higher temperature,Low T,High T,mixing free energy DGmix,XB,0,1,the absolute free energy is not of interest!,Chapter 1 : Thermodynamics and Phase Diagrams,1-27,1.3.3 Chemical Potential,Multi-Component System,dnA,constant T and P,t
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