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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
16、otal free energy of the system : G G + dG if dnA small enough, dG proportional to dnA, or : dG = mAdnA,Definition: Chemical potential , or Partial molar free energy,Note: G: total free energy of the system G: molar free energy (one mol),Chapter 1 : Thermodynamics and Phase Diagrams,1-28,geometric me
17、aning of chemical potential,A,B,XB,mA,mB,G,GB,GA,RT lnXA for ideal solution,RT lnXB for ideal solution,G,tangent line at XB,Chapter 1 : Thermodynamics and Phase Diagrams,1-29,Chapter 1 : Thermodynamics and Phase Diagrams,1-30,A-A,B-B,Before mixing,B,B,A,A,A-B,B,A,B,A,A-B,After mixing,eAA + eBB,2eAB,
18、Energy change per A-B bond : e = eAB - (eAA + eBB) AB bonds per mol : PAB = Na z XAXB Therefore : DHmix = w XAXB , where w = Na ze,0,DHmix,XB,1,w,Chapter 1 : Thermodynamics and Phase Diagrams,1-31,Chapter 1 : Thermodynamics and Phase Diagrams,1-32,Chapter 1 : Thermodynamics and Phase Diagrams,1-33,C
19、hapter 1 : Thermodynamics and Phase Diagrams,1-34,Chapter 1 : Thermodynamics and Phase Diagrams,1-35,1.4 Equilibrium in Heterogeneous Systems,Chapter 1 : Thermodynamics and Phase Diagrams,1-36,Chapter 1 : Thermodynamics and Phase Diagrams,1-37,Heterogeneous Equilibrium,Condition of Equilibrium in a
20、Heterogeneous System continue : about the common tangent line,A,B,a,P,and :,Chemical potentials of component A and B in a phase with the composition of,and :,Chemical potentials of component A and B in b phase with the composition of,b,Q,Chapter 1 : Thermodynamics and Phase Diagrams,1-38,1.5 Binary
21、phase diagrams,Chapter 1 : Thermodynamics and Phase Diagrams,1-39,Chapter 1 : Thermodynamics and Phase Diagrams,1-40,Chapter 1 : Thermodynamics and Phase Diagrams,1-41,1.5.4 Fe-Si System,Chapter 1 : Thermodynamics and Phase Diagrams,1-42,1.5.5 Fe-C System,Chapter 1 : Thermodynamics and Phase Diagram
22、s,1-43,1.6.1 The solid solvus,Equilibrium T1 :,For dilute solution of B in a :,1.6 Thermodynamics and Phase Diagrams,Chapter 1 : Thermodynamics and Phase Diagrams,1-44,Gibbs-Helmhotz equation:,Enthalpy change when 1 mol b-form B atoms dissolve in a phase to make a dilute solution,DHB : enthalpy diff
23、erence between the b-form B and a-form B W : energy change of a-form B dissolved into a phase,Therefore:,Chapter 1 : Thermodynamics and Phase Diagrams,1-45,Chapter 1 : Thermodynamics and Phase Diagrams,1-46,Chapter 1 : Thermodynamics and Phase Diagrams,1-47,Chapter 1 : Thermodynamics and Phase Diagr
24、ams,1-48,Chapter 1 : Thermodynamics and Phase Diagrams,1-49,1.7 Thermodynamics during Phase Transformations,Chapter 1 : Thermodynamics and Phase Diagrams,1-50,The driving force of solidification,Y0,Liquid,Solid a,L,S,P, T1,G,x,x,xL,xS,Q,Lever Rule,xS,xL,1 mol x, GP,initial,after equilibrium,xS mol x
25、S, GS,xL mol xL, GL,DG = GP - GQ,DG : per mol solution not per mol solid nuclei,R,xS mol xS, GR,DG = 0,DG1 = GR - GS,DG1 : per mol solid nuclei,Free energy change for 1 mol solution: DG1xS = DG,Chapter 1 : Thermodynamics and Phase Diagrams,1-51,The driving force of nucleation,Y0,Liquid,Solid a,L,S,P
26、, T1,G,x,x,xL,xS,Q,During nucleation, xL will not change. This means DG1 = GR - GS is not the nucleation driving force.,If we move point L to P, we see the free energy per mol nuclei will be at point T (insect point of the tangent line Y at P with xS).,R,T,Y,Chapter 1 : Thermodynamics and Phase Diag
27、rams,1-52,The driving force of nucleation,Y0,Liquid,Solid a,L,S,P, T1,G,x,x,xL,xS,Q,R,T,Y,DG2 = GT - GS is the driving force per mol nuclei with the composition of xS.,But the composition of initial nuclei could differ from xS, if larger driving force available other than xS.,T,S,x,Example: nuclei w
28、ith the composition of x have a driving force of GT - GS , which is larger than those at xS.,What is the maximal driving force ?,Chapter 1 : Thermodynamics and Phase Diagrams,1-53,The maximal driving force,Drawing a tangent line on the liquid G-curve at the original composition x, the mol driving fo
29、rce for nucleation equals to the distance between the tangent line and the solid G-curve at the nucleus composition.,DG will be even higher if x xN.,But will be decreased if the composition shifts further from xN to x.,The maximal driving force will be available for the nuclei having a composition a
30、t which the tangent on the solid G-curve (YN) parallels to that on the liquid G-curve at the original composition of the solution, i.e.:,Chapter 1 : Thermodynamics and Phase Diagrams,1-54,Chapter 1 : Thermodynamics and Phase Diagrams,1-55,Chapter 1 : Thermodynamics and Phase Diagrams,1-56,Summary,Chapter 1 : Thermodynamics and Phase Diagrams,1-57,Chapter 1 : Thermodynamics and Phase Diagrams,1-58,Chapter 1 : Thermodynamics and Phase Diagrams,1-59,Chapter 1 : Thermodynamics and Phase Diagrams,1-60,Chapter 1 : Thermodynamics and Phase Diagrams,1-61,End of Chapter 1,