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q1fall2004_key4324 - may know is a bit low After 2/52 years...

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Quiz 1 EMA 4324, LecSec 3009 KEY Friday, September 3, 2004 1. [5 points] Two cubes of iron, each 1.000 cm on a side [AW(Fe) = 55.85 g/mol. ρ (Fe) = 7.850 g/cm 3 were placed in a beaker containing 1000 cm 3 of stagnant seawater. After a week, one specimen was removed, then immersed in inhibited HCl [concentrated HCl + 50 g/L SnCl 2 + 20 g/L SbCl 3 ] until free of visible corrosion products. After drying, it was found to weigh 7.545 grams. What is its corrosion penetration rate [CPR] in mils per year [1 mil = 10 -3 inch]? *************************************************************************** m = 7.850-7.545 = 0.305g/[7.850g/cm 3 *6cm 2 *7d/365day/yr] = 0.338 cm/yr *[in/2.54cm]*1000mil/in = 133 mpy 2. [5 points] Assuming no change in corrodability or corrosivity, what would you expect the weight of the second cube to be when it was removed a week later [than the first]? *************************************************************************** Probably the easiest way to do this is to assume a constant CPR of 133 mpy [which, as you
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Unformatted text preview: may know, is a bit low]. After 2/52 years, the dimensions will be reduced by 2*133*2/52 or 10.2 mils, 0.0102 inches [0.026 cm]. Length of cube edge is now 1.000-0.026 = 0.974 cm, V = 0.924 cm 3 , mass = 0.924*7.850 = 7.253 g 3. [5 points] According to Jones, point “D” represents the “most accurate final coupon weight”. Just for the sake of causing trouble, suppose I were to take the position that “B” is the better coupon weight value. Based upon your perception of what it is that you are trying to do here [cleaning-wise], how and why, convince me that I am wrong [or not]. If the initial weight loss up to point B is due to removal of insoluble corrosion products and the weight loss beyond point B is due to removal of base metal, why on earth would you assume that base metal is being removed from the start of the cleaning process when base metal is still presumably being covered by corrosion product? Number of Cleaning Cycles [Cleaning Time] Weight Loss A B C D...
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