A carburizing gas at 1000 C maintains a 1.0% carbon concentration at the surface of a steel part whose initial carbon content is 0.2%. How long would it take to reach a carbon content of 0.5% at a depth of

(a) 1.2 mm from the surface, and

(b) 2.5 mm from the surface?

The diffusion coefficient of carbon in steel is 3.5 x 10-11 m2/s.

Q. 3. A porous solid was brought in contact with a liquid coating. The liquid was wicked in the pores. Using the property data give below, calculate the rate of penetration at the end of 2 min. from the start assuming pores to be straight capillaries of 10 micrometer diameter. Surface tension (σlv) of liquid: 0.80 N/m, contact angle: 22°, and viscosity: 0.0035 Pa.s. Will penetration rate increase or decrease with increasing time?

Q. 4 Calculate the energy in Joules required to evaporate liquid gold at its boiling point (2857 C) to form a 5 micrometer thick coating on all surfaces of a solid cylindrical disc of 4 cm diameter and 2 cm thickness. The vapor pressure – temperature relationship for liquid gold is:

The atomic weight of gold is 196.9, and the density of gold is 19.3 g/cc.

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