C3-Thermodynamics of unary materials-2哈尔滨工业大学 硕士生热力学课件.pdf

3.5 单元材料的两相平衡 Definitions and basic concepts Phase(相): A homogeneous portion of system that has uniform physical and chemical characteristics. (a(a deviationdeviation fromfrom homogeneityhomogeneity isis oftenoften allowed)allowed). Compponents((组元组元)): a chemical constituent ((element or compound) of an alloy, which may be used to specify composition. Phase diagram(相图): A graphical representation of the relationship between environmental constants (T, P.) , composition and regions of phase sttabilitbility usualllly undder conditidition off equilibilibriium. 3.5 单元材料的两相平衡 Iron- carbon phase diaggram (from Binary alloy phase diagrams, ASM Int., 1990) 推荐一本参考书： 王崇琳王崇琳, 相图理论及其应用相图理论及其应用 ((中国科学院研究生院教材中国科学院研究生院教材)), 高等教育出版社高等教育出版社66 3.5 单元材料的两相平衡 CriteriaCriteria forfor equilibriumequilibrium Equilibrium: a state of s system where the phase characteristics remain constant over indefinite time period. SpontaneousSpontaneous process(process( 自发过程自发过程)) AtAt equilibrium(equilibrium(平衡平衡)) Isolated systems S 0, Seq = Smax VV = 00, andand isothermalisothermal process:process: dF 0, Feq = Fmin Isothermal and isobaric process: dGdG 00, GGeq == GGmin 3.5 单元材料的两相平衡 单元材料的两相平衡：两种不同结构相之间的平衡问题。 两相平衡的条件两相平衡的条件： GG 00 GG GG m m 等温等压下，由一相变成另一相时， Gibbs 自由能的变化为零。OR 两相 共存时Gibbs 自由能相等。 3.5 单元材料的两相平衡 一个纯元素，通常以几种状态存在，如固态、液态和气态。 比较固态与液态的Gibbs 自由能差： 假