Question

To protect an iron (Fe) rod of radius of 20 cm from being oxidized, a layer of chromium (Cr) is coated. Suppose the oxidation rate constant for Cr and Fe is respectively 2.5x10 cm/sec and 2x10 cm/sec. It is assumed that the oxidation rate constant (K) of iron under chromium oxide coating remains the same as it is in direct contact with air. Determine what is the minimum thickness of Cr coating is needed to protect Fe for 5 years (365 days per year) from oxidation up to a maximum thickness of 2 cm (i.e., the maximum thickness of Fe20j allowed is 2 cm)'?

Answer 1

Solution Gvn thet The cuidasion ase yCon Stant +0 匕 N ouidadion Ro Con siant 62 5 XiOCm Sec 5xx 365 x24 x360o

2.5%(08 x 31536 00 -1 = 238 cm2 So Time -laken -for 그ton 238 8 63 3.79 님可