Introduction(2) S.J.T.U. Phase Transformation and Applications Page 6/42 Surface energy based on Gibbs free energy dG =-SaT +VdP ydA aG OH OF aA T.P A )sy S.P A Commonly observed manifestations A liquid droplet tries to minimize its free energy,it assumes a spherical shape Small droplets tend to agglomerate into larger droplets,minimizing their combined surface-to-volume ratios Small particles of metals or ceramics,when pressed into a shape and heated at high temperatures,will"sinter"into a solid mass. SJTU Thermodynamics of Materials Spring2008©X.J.Jin Lecture 20 surface
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2008 © X. J. Jin Lecture 20 surface Page 6/42 Introduction (2) Surface energy based on Gibbs free energy = − + + γdAVdPSdTdG A PT G , ⎟⎠⎞ ⎜⎝⎛ ∂∂ γ = Commonly observed manifestations A liquid droplet tries to minimize its free energy, it assumes a spherical shape Small droplets tend to agglomerate into larger droplets, minimizing their combined surface-to-volume ratios Small particles of metals or ceramics, when pressed into a shape and heated at high temperatures, will “sinter” into a solid mass. PT VS PS A VT F A H A U A G , , , , ⎟⎠⎞ ⎜⎝⎛ ∂∂ ⎟ = ⎠⎞ ⎜⎝⎛ ∂∂ ⎟ = ⎠⎞ ⎜⎝⎛ ∂∂ ⎟ = ⎠⎞ ⎜⎝⎛ ∂∂ γ =
Surface Energy Surface Tension S.J.T.U. Phase Transformation and Applications Page 7/42 Image a film of liquid stretched on a frame -dx- 21ydx =Fdx Film Y=F/21 Y Surface energy with units of Y←一≥f dynes per centimeter,or newtons per meter in the SI Soap film system. Y←—>f Detail of wire Figure 4.1 Stretching a film-increasing area. SJTU Thermodynamics of Materials Spring2o08©X.J.Jin Lecture 20 surface
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2008 © X. J. Jin Lecture 20 surface Page 7/42 Surface Energy / Surface Tension Image a film of liquid stretched on a frame 2 γ = Fdxdxl γ = 2/ lF γ Surface energy with units of dynes per centimeter, or newtons per meter in the SI system. dx
Surface Energy Surface Tension S.J.T.U. Phase Transformation and Applications Page 8/42 Surface energy with units of dynes per centimeter,or newtons per meter in the SI system. [界面张力] [界面能] SI单位制 N(牛顿)·m-1=J(焦耳)m-2 cgs单位制 dyn(达因)，cm-1=erg(尔格)·cm-2 SJTU Thermodynamics of Materials Spring2008©X.J.Jin Lecture 20 surface
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2008 © X. J. Jin Lecture 20 surface Page 8/42 Surface Energy / Surface Tension γ Surface energy with units of dynes per centimeter, or newtons per meter in the SI system
Surface Energy Surface Tension(1) S.J.T.U. Phase Transformation and Applications Page 9/42 Surface tension or surface energy Liquid Isotropic Surface energy does not change as the surface is stretched Solids Function of the crystallographic plane that is expected The nature of a solid surface changes as the material is deformed. SJTU Thermodynamics of Materials Spring 2008 X.J.Jin Lecture 20 surface
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2008 © X. J. Jin Lecture 20 surface Page 9/42 Surface Energy / Surface Tension (1) Surface tension or surface energy Liquid Isotropic Surface energy does not change as the surface is stretched Solids Function of the crystallographic plane that is expected The nature of a solid surface changes as the material is deformed
纯物质的表面能和各种界面能 S.J.T.U. Phase Transformation and Applications Page 10/42 口△◇0固体 W e▣液/液 3 ■▲◆●液体 3 ⊙固/液 Al2O3/LFe Fe ⊙ Cu 晶界 日 Mgo SiO,/LFe 金属 Al A203 纯金属的 Fe Hg Ge Si 随机晶界 Cu 0.3 Sb 0.3 Al 类金属 SiOz Fe 无机化合物 NaCl 纯金属的 Cu 0.1 0.1 --- 固/液界面 回 AH2O Al 甘油 尼龙 e LCu/LPb 0.03甲醇 0.03 有机化合物 石蜡 Hg 石蜡/H20 特弗伦 0.0 0.01 100 300 1000 3000 100 300 1000 3000 熔点，Tm/K 熔点，Tm/K (a)纯物质的表面能 (b)各种界面能 图5.1 (a)固体或液体的表面能（金属最大，塑料最小）；(b)固/液或 液/液界面能和随机晶界能（因物质组合的不同而变得多种多样） From T.Nishizawa SJTU Thermodynamics of Materials Spring2008©X.J.Jin Lecture 20 surface
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2008 © X. J. Jin Lecture 20 surface Page 10/42 纯物质的表面能和各种界面能 From T. Nishizawa