Investigation On Mechanism Of Influence Of Semiconductor Fillers On Corrosion Behavior Of Metals

Semiconductor oxide materials have been widely used as coating fillers,which confer the coatings with superior functional properties such as thermal conductivity,UV resistance and antifouling properties.However,the possibility that semiconductor fillers would accelerate corrosion of metal is often ignored.The semiconductor filler may directly contact with the metal substrate when the coating is damaged,inducing"micro-galvanic corrosion"between the semiconductor filler and the metal substrate and aggravating the corrosion of the metal substrate.Therefore,the semiconductor filler may possess a significant effect on the corrosion behavior of the metal substrates at the coating defect.Up till now,there have been few reports on corrosion promotion activity of semiconductor fillers.Starting from the problem that semiconductor fillers can accelerate the corrosion of metal substrates,this paper investigates the electrochemical properties of the prepared semiconductor coatings after failure and analyzes the mechanism of influence of semiconductor fillers on corrosion behavior of metals,based on which a selection criterion of semiconductor materials as coating fillers is also proposed.The main contents of this paper include the following aspects:（1）The effect and mechanism of different types of semiconductor fillers on the corrosion behavior of metal substrates were studied.In this work,common semiconductive fillers including TiO₂,Fe₂O₃ and Cu₂O were prepared and incorporated into polyvinyl butyral coatings,then investigated the effect of these three semiconductors on corrosion behavior of metal substrates.Results of electrochemical measurement revealed that TiO₂ and Fe₂O₃ accelerated the corrosion of metals,while Cu₂O did not influence the corrosion of metals.Considering factors that influence the resistance of electron transfer between the fillers and the metal substrates and the consumption rate of electron participating in cathodic reduction reaction that occurs on the surface of fillers,a micro-galvanic corrosion mechanism based on work function difference between semiconductor and metal and oxygen reduction reaction activity was proposed to explain the corrosion promotion phenomenon.（2）The effect and mechanism of different phase morphology TiO₂ fillers on the corrosion behavior of metal substrates were studied.Three types of TiO₂ materials with different crystal forms and crystal faces were prepared,and the influence of different crystal forms and crystal faces of semiconductor on corrosion promotion activity was studied.This work revealed that rutile TiO₂ has no effect on the corrosion behavior of metal substrate,while anatase TiO₂ can accelerate the corrosion of the metal substrate,and the corrosion reactions of anatase TiO₂exposed on the 001 surface was more active and intense than others.The mechanism of corrosion promotion activity was verified from both the work function difference between semiconductor and metal and the oxygen reduction reaction activity of the semiconductor fillers.