上海交通大学：《材料热力学 Thermodynamics of materials》课程教学资源（课件讲稿）Chapter11 Surface and Interface

上海交通大学 1856 SHANGHAI JIAO TONG UNIVERSITY Chapter 11.Surface and Interface Surface energy surface tension Effect of surface curvature ·Vapor pressure Solubility of small particles Wetting of surfaces ·Gibbs absorption isotherm Review

Chapter 11. Surface and Interface Review

上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY Introduction:Surface Surfaces and Interfaces Everything is made of something and has to end somewhere. An atom at a free surface of a solid has greater energy than an atom in the interior of a crystal because it is less tightly bound. Surface energy The sum of all the excess energies of the surface atoms Can be defined in terms of energy,enthalpy, Helmholtz free energy,or Gibbs free energy, depending on the physical constraints placed on (a)由劈开晶体形成的自由键 the definition

Introduction: Surface

上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY Introduction:Surface energy Surface energy based on Gibbs free energy dG =-SdT+VdP ydA OF TP A T.P 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

Introduction: Surface energy

上游充通大粤 SHANGHALIIAO TONG UNIVERSITY Barerett Media

上游充通大￥ SHANGHAI JIAO TONG UNIVERSITY Introduction:Surface energy Image a film of liquid stretched on a frame dx- 21ydx Fdx y=F/21 Y Surface energy with units of 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

Introduction: Surface energy

上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY Surface energy surface tension Y 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)·m1=J(焦耳)m-2 cgs单位制 dyn(达因)·cm-l=erg(尔格)·cm-2

Surface energy / surface tension

上游充通大￥ SHANGHAI JIAO TONG UNIVERSITY Surface energy surface tension Surface tension or surface energy Liquid Isotropic Surface energy does not change as the surface is stretched Solids Function of the erystallographic plane that is expected The nature of a solid surface changes as the material is deformed

Surface energy / surface tension

上游充通大￥ SHANGHAI JIAO TONG UNIVERSITY Surface energy of materials 口△◇0固体 ▣液/液 3 ■▲◆●液体 Al2O3/LFe Fe 。固/液 ⊙ 品界 ⊙ Mgo SiOz/LFe 金属 、 纯金属的 Fe Hg t-w.r/o 随机晶界 Cu 0.3 0.3 类金属 SiOz 无机化合物 纯金属的 Cu NaCl 乐 0.1 0.1 固/液界面 AH2O 目 甘油 尼龙 LCu/LPb 0.03甲醇 0.03 有机化合物 石蜡 Hg 石蜡/H2O 特弗伦 0.01 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）

Surface energy of materials

上游充通大￥ SHANGHAI JIAO TONG UNIVERSITY Approximate Calculation of Solid Surface Energy(1) The binding energy of an atom to a solid is the result of discrete bonds to its nearest neighbors,then the energy of one bond,s,can be written as follows: △Hs S= 0.5ZNA AHs The molar enthalpy of sublimation (breaking all the bonds) Z The coordination number N,Avogadro's number There are 0.5ZNA bonds per mole

Approximate Calculation of Solid Surface Energy (1)

上浒充通大粤 SHANGHAI JIAO TONG UNIVERSITY Approximate Calculation of Solid Surface Energy (2) If we cleave a face-centered cubic crystal along a(111)plane,three bonds per atom will be broken.Two surfaces formed,the work required to form the surfaces will be 38/2 per surface atom. 3 W= △Hs V6/4a (for Z=12) △Hs E 2 ANA 0.5ZN4 △Hs Y= v2/2ao 4N, aov 2 N/A is the number of atoms per unit (Face diagonal) area.For fec structure: Figure 4.2 Atomic packing on the (111)face of a face-centered N 4 cubic crystal. A 2,* A/N= a=3a2 4 4

Approximate Calculation of Solid Surface Energy （2）