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Posted: 2/6/2006 6:11:02 PM EDT
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
Link Posted: 2/6/2006 6:13:42 PM EDT
It seems like Do for Fe in FCC Fe is smaller than for the same system in BCC.

However, Do for C in FCC Fe is larger than for the same system in BCC.

Why is this? Is there a pattern?
Link Posted: 2/6/2006 7:40:26 PM EDT
@ "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....
Link Posted: 2/6/2006 7:57:53 PM EDT
Correct but I already know that.
Link Posted: 2/7/2006 7:22:03 AM EDT
btt
Link Posted: 2/7/2006 5:24:01 PM EDT
btt
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