If D = 0.00001 cm^2/s (for oxygen through water), how long would it takes the ox

Question

If D = 0.00001 cm^2/s (for oxygen through water), how long would it takes the oxygen to diffuse 0.01 cm below the surface of a still pond? 0.l cm? 1 cm? Based on your answer, do you think it would really take calculated amount of time for oxygen to diffuse in to water? What would happen to fish hanging at 1 cm below the water surface? The diffusion coefficients for copper and aluminum at 500 and 600 4.8 times 10^-4 and 5.3 times 10^-13 m^2/s, respectively. Determine the approximate time at 500 will produce the same diffusion result (in terms of concentration of Cu at point in Al) as 10 hour heat treatment at 600 degree C.

Explanation / Answer

1)T = x2/2D

T0.01 = (0.01)2/2*0.00001 = 5 s

T0.1 = (0.1)2/2*0.00001 = 500 s

T1 =  (1)2/2*0.00001 = 50000 s = 833.33 s

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2)

D*t = constant

D500t500 = D600t600

=> t500 = (5.3*10-13)(10) / (4.8*10-14)

=> t500 = 110.4 hrs

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