A sheet of steel 1.8 mm thick has nitrogen atmospheres on both sides at 1200 deg

Question

A sheet of steel 1.8 mm thick has nitrogen atmospheres on both sides at 1200 degree C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6 x 10^-11 m^2/s, and the diffusion flux is found to be 1.2 x 10^7 kg/m^2.s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3. How far into the sheet from this high-pressure side will the concentration be 2.0 kg/m^3 ? Assume a linear concentration profile.

Explanation / Answer

Flux Nc   = - D * dC / dx

1.2 * 10^-7 = - 6 * 10^-11    * dC/dx

dC / dx = -2000

C(x)    = -2000x + Co

at x = 0    C(0) = 4

C(x)   = -2000 * x + 4

Therefore at

2   = -2000 * x + 4

x = 2 / 2000 = 1 mm

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.