Grain boundary passivation

Seager, C.H., and Ginley, D.S., (1982). Fundamental Studies of Grain Boundary Passivation in Polycrystalline Silicon with Application to Improved Photovoltaic Devices, Sandia Report, SAND82-1701, p. 19-21. 

Solid A Solid B S/S Corrosion, grain boundary passivation, adhesion, delamination, epitaxial growth, nucleation and growth abrasion, wear, friction, diffusion, boundary structure thin films, solid state devices, mechanical stability, creep. 

Fig. 4. EBIC micrographs illustrating depth of grain boundary passivation. Hydrogen ions were incident from the top. (a) Shows a typical boundary before any passivation (b) and c) show other boundaries after hydrogen passivation. 

From polarization curves the protectiveness of a passive film in a certain environment can be estimated from the passive current density in figure C2.8.4 which reflects the layer s resistance to ion transport tlirough the film, and chemical dissolution of the film. It is clear that a variety of factors can influence ion transport tlirough the film, such as the film s chemical composition, stmcture, number of grain boundaries and the extent of flaws and pores. The protectiveness and stability of passive films has, for instance, been based on percolation arguments [67, 681, stmctural arguments [69], ion/defect mobility [56, 57] and charge distribution [70, 71]. 

The following mechanisms in corrosion behavior have been affected by implantation and have been reviewed (119) (/) expansion of the passive range of potential, (2) enhancement of resistance to localized breakdown of passive film, (J) formation of amorphous surface alloy to eliminate grain boundaries and stabilize an amorphous passive film, (4) shift open circuit (corrosion) potential into passive range of potential, (5) reduce/eliminate attack at second-phase particles, and (6) inhibit cathodic kinetics. 

Sometimes the formation of oxide films on the metal surface binders efficient ECM, and leads to poor surface finish. Eor example, the ECM of titanium is rendered difficult in chloride and nitrate electrolytes because the oxide film formed is so passive. Even when higher (eg, ca 50 V) voltage is apphed, to break the oxide film, its dismption is so nonuniform that deep grain boundary attack of the metal surface occurs. 

Potentiostatic methods, being capable of detecting differences in corrosion and passivation behaviour of various parts of a heterogeneous surface, have been applied to the electrochemical determination of grain boundary corrosion... 

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