Research On Metal Corrosion Mechanism Of Semiconductor Material/Metal Galvanic System

Semiconductor materials are widespread in the field of metal corrosion and protection.On the one hand,the corrosion resistance of the coating is improved by adding semiconductor fillers;on the other hand,most of the corrosion products on the metal surface have semiconductor properties.The difference in the electronic structure characteristics between semiconductors and metals changes the electron transport characteristics of the semiconductor/metal phase interface,thereby affecting the corrosion behavior of metals.Therefore,two types of semiconductor material/metal galvanic systems were selected in this paper to study the influences of semiconductor materials on metal corrosion behavior.Based on the electron transfer path of the corrosion process and the nature of the semiconductor materials,the corrosion mechanism of semiconductor material/metal galvanic system was also analyzed in depth,and provides theoretical support for the establishment of the basis for judging the"corrosion-promotion activity"of semiconductors.The main research conclusions are as follows:（1）For TiO₂ semiconductor/Cu system,three kinds of TiO₂ semiconductor fillers and corresponding composite coatings were prepared,and the influences of different crystal structure TiO₂ semiconductor fillers on copper corrosion were investigated.The results show that the work function of copper（4.66 eV）is lower than that of the two anatase TiO₂（5.13 eV,5.20 eV）,and higher than that of rutile TiO₂（4.54 eV）.The three types of TiO₂ are all n-type semiconductors,and their electrical conductivities and oxygen reduction activities decrease in the order of anatase TiO₂ with（001）facets exposed,anatase TiO₂,and rutile TiO₂.For copper-based composite coating systems,anatase TiO₂,especially anatase TiO₂ with（001）facets exposed,exhibits strong"corrosion-promotion activity"to copper,while the rutile TiO₂does not clearly exhibit the characteristic.（2）For iron oxide semiconductor/Fe system,five kinds of iron semiconductor corrosion products were selected and made into Fe/corrosion product composite electrodes.The influences of semiconductor corrosion products on iron corrosion behavior were investigated.The results show that the work functions of iron corrosion products areβ-FeOOH（5.07 eV）,Fe₂O₃（5.06 eV）,Fe₃O₄（4.99 eV）,γ-FeOOH（4.90 eV）,α-FeOOH（4.89 eV）,which are all higher than the work function of iron（4.62 eV）.The corrosion products are all n-type semiconductors,and their electrical conductivities decrease in the order of Fe₃O₄,β-FeOOH,Fe₂O₃,γ-FeOOH andα-FeOOH;their oxygen reduction reaction activities decrease in the order ofβ-FeOOH,Fe₂O₃,Fe₃O₄,γ-FeOOH andα-FeOOH.In the Fe/corrosion product composite electrode system,except forα-FeOOH,the other corrosion products all exhibit"corrosion-promotion activity"to iron,and the characteristics decrease in the order ofβ-FeOOH,Fe₂O₃,Fe₃O₄,andγ-FeOOH.（3）In a semiconductor/metal galvanic system,the work function and type of the semiconductor material determine the direction of electron transfer at the metal/semiconductor interface,and thus determine whether the semiconductor material has"corrosion-promotion activity"to metal.When the semiconductor material is an n-type semiconductor and its work function is higher than that of metal,the metal/semiconductor phase interface forms an ohmic contact,and electrons tend to transfer from the metal to the semiconductor to promote corrosion anode reaction,thereby exhibiting"corrosion-promotion activity".On the contrary,the"corrosion-promotion activity"cannot be exhibited.The conductivity and oxygen reduction reaction activity of the semiconductor material affect the rate of electron consumption at the semiconductor/solution interface,which affects the corrosion cathode reaction and the intensity of the"corrosion-promotion activity".