ENG 2002 Lecture Notes - Carburizing, Astm International, Activation Energy
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Assignment #3: Imperfections and Diffusion
1. Calculate the fraction of atom sites that are vacant for lead at its melting temperature of 327oC.
Assume an energy for vacancy formation of 0.55 eV/atom.
2. Calculate the activation energy for vacancy formation in aluminum, given that the equilibrium
number of vacancies at 500oC is 7.57x1023 m-3. The atomic weight and density (at 500oC) for
aluminum are, respectively 26.98 g/mol and 2.62 g/cm3.
3. What is the composition, in atom percent, of an alloy that consists of 30 wt% Zn and 70 wt%
4. For an ASTM grain size of 8, approximately how many grains would there be per square inch
(a) at a magnification of 100x, and (b) without any magnification?
5. Compute the number of kilograms of hydrogen that pass per hour through a 5-mm-thick sheet
of a palladium having an area of 0.20 m2 at 500oC. Assume a diffusion coefficient of 1.0x10-8
m2/s, that the concentrations at the high- and low-pressure sides of the plate are 2.4 and 0.6 kg of
hydrogen per cubic meter of palladium, and that steady-state conditions have been attained.
6. Determine the carburizing time necessary to achieve a carbon concentration of 0.45 wt% at a
position 2 mm into an iron-carbon alloy that initially contains 0.2 wt% C. The surface
concentration is to be maintained at 1.3 wt% C, and the treatment is to be conducted at 1000oC.
The data for iron is Do=5.0x10-5 and Qd=284 KJ/mol or 2.94 eV/atom.
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