The Slope of Dislocation Etch Pits

The slope of etch pits is determined by the normal and tangential etch rates, given by (46), 

It is easy to see from this relation that with an increase in An, the pit slope first increases to a maximum value at An, and finally decreases again. However, f or A/i An, depending on the behavior ofj8, the pitslope may even increase with An. The factor j8 Is largely determined by the dissolution kinetics which are governed by the potential difference A/i andadsorption processes taking place on crystal surface. 

The above considerations hold good for fresh dislocations. Several experimental results, however, show that the segregation of impurities at dislocations facilitates the process of etch-pit formation. This behavior is associated with the fact that impurity segregation leads to an increased potential difference and decreases the free-energy change required for the formation of critically-sized two-dimensional nuclei. In such cases, the size and slope of etch pits can vary from those at fresh dislocations, if Vp Vp. This feature may be understood from the model given by Ives and McAusland (47). 

Under steady-state conditions when the etch pits are formed at a constant 

For pits at different defects (different v ) produced by the same etchant (constant Vp and v,), a piot of m against (D/t) wili be a straight line. The values of v, and Vp may be estimated from the slope and intercept of the straight line. 

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