MitX Solid-State ungraded question- (Diffusion!)

Question

jadedry · Answer

I'm taking the online course, and I came across a practice question I have no idea how to solve can someone please provide hints?

Thanks in advance!

--

During the heat treatment of a skateboard axle made of carbon steel (an iron alloy with 0.6% C) a person who has obviously not taken 3.091 incorrectly sets the gas composition so as to cause a loss of carbon for the alloy. The axle was placed in a furnace at 1250∘ C where the effective surface concentration of carbon was zero. At what depth has the carbon concentration fallen to 1/4 of the initial concentration after 1 hour? Assume the diffusivity of carbon is 3.091×10−6 cm2/sec.

Give your answer in terms of micrometers.

jadedry · Answer

So, I know I need to use Ficks Second law which is ?time dependant? But I have a feeling I need to use another equation and I'm not sure which one.