4. (a) Name industrialprocesses in which:
Diffusion in the solid is essential.
Diffusion in the solid must be prevented.
(b) Why are the steel gears case hardened? (5p).
(c) For a 1020 steelit has been determined that a carburizing treatment of 15 hrduration at 900 0C will raise the carbon concentrationto 0.35 wt% at a point 2.0 mm from the surface. Estimate the timenecessary to achieve the same carbon concentration at a 6.0 mmposition from the surface for the same steel and at the samecarburizing temperature.
