After a 27-hour heat treatment at 1050â°c (and subsequent cooling to room temperature), the concentration of a is 3.1 wt% at the 15.4-mm position within metal b. if another heat treatment is conducted on an identical diffusion couple, this time at 840â°c for 27 hours, at what position will the composition be 3.1 wt% a? the preexponential and activation energy values for the diffusion of a in b are 2.7 ã 10-6 m2/s and 160 kj/mol, respectively.