当前位置:首页 >> 教育学/心理学 >>

APCCC会议文章摘要 0068


Passivity: The Enabler of Our Metals-Based Civilization
Digby D. Macdonald Center for Electrochemical Science and Technology Department of Materials Science and Engineering Pennsylvania State University University Park, PA 16802 and Chair Professor Research Institute King Fahd University of Petroleum and Minerals Dhahran, Saudi Arabia For more than forty years, the conditions for the existence of the passive state, and hence for the existence of our metals-based civilization, which is based upon the use of the reactive metals (Al, Cr, Fe, Ni, etc) to build machines, have been described in terms of equilibrium thermodynamics in the form of Pourbaix diagrams. These diagrams plot equilibrium potential versus pH relationships for various reactions (e.g., Fe/Fe 3 O 4 , Fe/Fe2+, Fe 3 O 4 /Fe2+) to define regions of stability or predominance. However, Pourbaix diagrams provide an equilibrium view of passivity, whereas passive films are nonequilibrium structures, whose existence depends upon an appropriate relationship between the rate of formation and the rate of destruction. Accordingly, a more accurate and realistic description of the phenomenon of passivity must be found in the field of electrochemical kinetics. It is this kinetic theory for depassivation (loss of passivity) that is presented in this paper. It is shown that the kinetic theory for depassivation not only accounts for transpassive dissolution, acid depassivation, flow-assisted corrosion, and fretting corrosion, but it also led to the discovery of a new form of depassivation, which is termed “resistive depassivation”. This form of depassivation results from the passage of the passive current through a resistive outer layer to a remote cathode, such that when the IR potential drop is subtracted from the control voltage, there is insufficient voltage drop across the barrier layer to maintain a finite thickness. In that case, the barrier layer disappears and the surface becomes “depassivated”. The kinetic theory of depassivation has led to the construction of Kinetic Stability Diagrams (KSDs), which the author offers as kinetic alternatives to the classical, equilibrium Pourbaix diagrams for describing the passive state.


赞助商链接
相关文章:
更多相关标签: