5.10 Show that
In this expression, when the x = 0 position is taken as the initial diffusion couple interface, then C1 is the impurity concentration
for x 6 0; likewise, C2 is the impurity content for x 7 0.
B x2
Cx= 1Dtexp a-4Dt b
is also a solution to Equation 5.4b. The pa- rameter B is a constant, being independent of both x and t.
5.11 Determine the carburizing time necessary to achieve a carbon concentration of 0.30 wt% at a position 4 mm into an iron-carbon alloy that initially contains 0.10 wt% C. The surface concentration is to be maintained at 0.90 wt% C, and the treatment is to be conducted at
A diffusion couple composed of two platinum-gold alloys is formed; these alloys have compositions of 99.0 wt% Pt-1.0 wt% Au and 96.0 wt% Pt-4.0 wt% Au. Determine the time this diffusion couple must be heated at 1000°C (1273 K) in order for the composi- tion to be 2.8 wt% Au at the 10 mm position into the 4.0 wt% Au side of the diffusion cou- ple. Preexponential and activation energy values for Au diffusion in Pt are 1.3 X 10-5 m2/s and 252,000 J/mol, respectively.