The wear resistance of a steel shaft is to be improved by hardening its surface by increasing the nitrogen (N) content within an outer surface layer as a result of nitrogen diffusion into the steel; the nitrogen is to be supplied from an external N-rich gas at an elevated and constant temperature. The initial N content of the steel is 0.0025 wt%, whereas the surface concentration is to be maintained at 0.45 wt%. For this treatment to be effective, a N content of 0.12 wt% must be established at a position 0.45 mm below the surface. (a) Will this process be a steady state or non-state process? Why?

Non steady state process

Because D ∝ 1/t

Explanation:

Here we have

Where:

= 0.0025 % by weight of N

= 0.45 % by weight of N

 = 0.12 % by weight of N

Therefore,

From the inverse erf function we have

Since x = 0.45 mm, we have

and

Dt = 8.069×10⁻⁸ m²

For steady state

Since Dt = 8.069×10⁻⁸ m² = Constant, then as the time increases the diffusion rate decreases hence the process is not steady state.

D is inversely proportional to t.

can you make it more obvious. i can't see it properly

answer:

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