The Kirkendall effect
is the migration of markers that occurs when markers are placed at the interface between an alloy
and a metal
, and the whole is heated to a temperature where diffusion
is possible; the markers will move towards the alloy region.
For example, using molybdenum
as a marker between copper
alloy), molybdenum atoms
will migrate towards the brass.
This is explained by assuming that the zinc diffuses more rapidly than the copper, and thus diffuses out of the alloy down its concentration gradient. Such a process is impossible if the diffusion is by direct exchange of atoms.