The Research Of Semiconducting Properties Of The Passive Film Formed On 304 Stainless Steel In Seawater

It is well known that the stainless steel has the good anticorrosion property for the thin and steady passive film formed spontaneously on the surface(generally lower than 10nm). But in the marine environment, it is easy to happen localized corrosion, what was worse is around by microorganism, so the stainless steel will breakdown if immersed in seawater for a long time, bringing so much damage to the human and the country.The thesis based on the semiconductor theory and electrochemical corrosion science, and by the method of electrochemical measurement and the Mott-Schottky, testing the capacitance-potential and making the Mott-Schottky plots to get the values of donor density(ND),flat-band potential(Vfb),Schottky potential(Vs) and the type of semiconductivity, and etc, so that speculate on the semiconducting properties. But there is little report about researching the relationships between the anticorrosion and semiconductivity by the method of C/E in the seawater. So it is important significance to research the validity of the method and the relationships between the anticorrosion and semiconductivity. The main work and conclusions as follows:1. the thesis testifies the validity of the Mott-Schottky to research the semiconducting properties of the passive film in the seawater medium by theory and experiment; and then explore and explain the dependence between the capacitance and frequence.2. the thesis researches the semiconducting properties of the passive film formed on the 304ss in seawater by the measurement of C/E. As can be seen from the results, in the range of above the Efb , the passive film exhibits N-type semiconductivity, and below the Efb , it behave as P-type. Furthermore, the Efb and point defect density are calculated by the equation of Mott-Schottky. Efb =-0.424V, ND=8.47×10²³.3. this report exhibits the relationships between the anticorrosion and semiconducting properties of the passive film in the seawater by measuring the EIS and Mott-Schottky at different film formation potentials. It is proved that the point defect density is the key parameter to the ability of anticorrosion. The more the point defect density, the stronger the ability of anticorrosion. Furthermore, 304ss has the best protective potential range in the passive region in the seawater. And it is the first time to calculate the values of the slop,ND,Efb,dOX and diffusion constant D0 at different film formation potentials in the seawater, analysis quantitatively the relationships between the anticorrosion and semiconducting properties of the passive film, D0 =2.01×10^-21cm²/s.