The Effect Of Different Factors On The Characteristics And Chemical Composition Of Passive Film Formed On 316L Stainless Steel

Stainless steel has been widely used in all walks of life for its outstanding anticorrosive property.The structure and performance of the passive film on the stainless steel surface can effectively influence the anticorrosive property of steel substrate indicating the importance of the research on the passive film.In this work,the electrochemical performances and the composition of passive films were studied by using electrochemical measurements and surface analysis techniques,respectively.And the point defect model was used to analyze the anticorrosion mechanism.The main research contents contain(1)the changes of properties and composition of passive film on stainless steel with passivation time;(2)the effect of N content in stainless steel,pH,temperature and salt concentration of solution on the characteristics of passive film;and(3)the performance and composition of passive films formed in high-temperature and high-salinity environment.The results show that the thickness,performance and composition changed with the increasing of passivation time.When the passivation time up to 25 days,the passive film is still growing.The noteworthy difference among the passive films formed with various passivation time is the composition and distribution of FeOOH in the passive films.With the prolonging of passivation time,the FeOOH could penetrate deeply into the film,and its concentration in the film could increase simultaneously.The anticorrosion properties of passive films could be promoted by increasing the N content within a certain concentration range.N exists in passive film as N3-,which can occupy the oxide vacancies at the metal/passive film interface and the hydroxyl vacancies at the inner/outer layer interface of the film due to its charge neutrality finally resulting in the decrease of the density of defects in film and the promotion of the corrosion resistance of the steel.The properties of passive films on stainless steels with and without N could be affected by the pH,temperature and salt concentration of solution,and the pH of solution could also influence the semiconductor properties of passive films.The corrosion resistance of films decreased with the temperature and salt concentration increasing.After preparing the passive films at a relative high temperature,the electrochemical impedance value of film with N was higher than that without N.The increasing of the salt concentration in the solution could slightly and significantly influence the electrochemical impedance values of the passive films with and without N,respectively.The passive films with and without N formed in high-temperature and high-salinity environment both had a n-type semiconductor property,but the performance of the film with N was better than that without N.The N can concentrate in passive film resulting in a good performance of the film.