Posted: 2/6/2006 6:11:02 PM EDT
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This isn't for school so please don't bash me for "not doing my homework." Why does the temperature independent factor Do get smaller for C in Fe and H in Fe. I'm talking about the equation: D = Do * e ^ (Q/KT) Also, is Do dependent on weither the host metal is BCC or FCC? I'm interested in the following systems Fe in FCC Fe Fe in BCC Fe C in FCC Fe C in BCC Fe H in FCC Fe H in BCC Fe I have an old textbook but it doesn't say much about this. I know Fe in Fe is a vacancy diffusion and C/H in Fe are interstitial diffusion. I know it takes less activation energy for intersitial diffusion. Scott |
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@ "low" temperatures, the equilibrium phase of Fe is ferrite, or alpha-Fe, a bcc structure. @ "high" temperatures, it's austenite (gamma-Fe), fcc fcc is a "close pack" structure, whereas bcc is not. Simply put, there's more displacement of Fe atoms to allow C and H to diffuse interstitially. On the other hand, the system I work with most often is Si, with either B or P diffusion.... 
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