金属腐蚀 英文PPT.pptxVIP

Material DegradationCatalogCorrosion Mechanism 1.1 thermodynamics 1.2 kinetics 2.Corrosion morphology 2.1 general corrosion 2.2 local corrosionthermodynamicsMechanism Material Degradation：Chemical reaction or electrochemical reaction reacted in metals，result in changing from simple substance to compoundThe reaction happen or not corrosion thermodynamicsThe speed of reactioncorrosion kineticsthermodynamicsFree energyFree energyΔG：it can be used to estimate whether the reaction can occur or not We can see，Pt and Au which ΔG0 no corrosion The orthers ΔG 0 corrosion thermodynamicsExampleThe reaction tendency increases?the ? ΔG is more largeThe reaction rate increasesEg.Al ?conduitFe ?conduitAl在大气中腐蚀倾向性比Fe大, 但Al的腐蚀速度却比Fe慢得多, 这是因为Al表面生成一层保护膜, 铁锈无保护作用, 或者说Al腐蚀反应的活化能比Fe 大得多thermodynamicsElectric series becauseΔG= ? nEF E=φ正 ? φ负so, whether the reaction occur or not can also be estimated by eletric series low potential + high potentialprimary batteryThe electric series can also be used to estimate whether the metal can be corroded in H or OEg. CuthermodynamicsE-pH diagramSo, as for reactions with H, potential associated with pH图中斜线表示有H+参与的反应,水平线表示没有H+参与。由图可知, 电位低至一定值,铁进入免蚀区而不被腐蚀, 这是阴极保护的理论依据pH=9~13时, 升高电位铁进入钝化区, 这是阳极保护理论依据强碱性时, 铁易生成HFeO3- 而被腐蚀thermodynamicsE-pH diagramuse value：1.To estimate whether the metal can be corroded in some specified conditions2.To estimate the product composition of the corrosion3.To estimate the conditions of slowing corrosionshortcoming：1.Can not estimate the reaction rate2.Can not estimate the concrete condition of the production3.E-pH diagram may engender deviationkineticsCorrosion cellThermodynamics: to asssessment reaction possibilitieskinetics: to estimate reaction ratesDifferent metalsSame metal different partsInhomogeneous featurepotential differenceprimary battery电位较低部分构成阳极, 其反应为金属的离子化:M=Mn ? ne.溶液中经常存在几种吸收电子的作用: 如溶有氧, 含H+或其他氧化剂（Fe3+,Ag+）,当阴极电子被吸收后, 电子就源源不断地从阳极流往阴极, 结果阳极金属不断被腐蚀kineticsCorrosion cellObviously, the