Constants and Corrosion Rates

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markmai86 Associate Join Date: Jun 2009 Posts: 43	Constants and Corrosion Rates 09/08/2009 11:40 AM
	Hello, I am currently dealing with constants I have never heard of before, especially the rate constant for oxydation and sulfidation of metal: kp. The units are g^2 cm^4 s^-1 and I can't visualize what it really means... I understand that the time is in there because the metal corrodes in a certain time. But I don't understand why the mass is squarred and why we have centimeters with a power of -4... I thought corrosion rates were just a corroded amount of metal for a certain surface during a certain time (so something like grams.centimeters^-2.seconds^-1) Here is a graph representing variations of this rate with variable pressures of sulfur (for sulfidation and not corrosion): Thank you.
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Milo Guru Join Date: Jul 2006 Location: "Dancing over the abyss." Posts: 4884 Good Answers: 243	#1 Re: Rate constant (sulfidation) units 09/08/2009 2:25 PM
	Here's a try: See equation X.22 p 440, and it s discussion; also appendix A.1 andA.2 p. 512 Here: http://books.google.com/books?id=TXoFThrTTEgC&pg=PA512&lpg=PA512&dq=oxidation+constant+(units)&source=bl&ots=pc8gBS_VNP&sig=1pbLjbhBrKDTn5O6x3FXTTA6Y_c&hl=en&ei=-ZemSoL4BYnjnAeN1eG7Bw&sa=X&oi=book_result&ct=result&resnum=5#v=onepage&q=oxidation%20constant%20(units)&f=false I am not familiar enough to explain this to you, but can mention in passing that we used the Pilling Bedworth Equation (ratio?) to predict scale film properties on various metals. If you look at this closely you will see that th e base factor is really momentum gram centimeter per second (g · cm/s or g · cm · s ^-1 ) milo __________________ People say between two opposed opinions the truth lies in the middle. Not at all! Between them lies the problem, what is unseeable,eternally active life, contemplated in repose. Goethe
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markmai86 Associate Join Date: Jun 2009 Posts: 43	#3 In reply to #1 Re: Rate constant (sulfidation) units 09/08/2009 4:01 PM
	Well thank you. I think the relation I needed is A.2. and that equation is where the constant is from...
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Mikerho Guru Join Date: Jan 2007 Location: Moses Lake, WA, USA, Thulcandra - The Silent Planet (C.S. Lewis) Posts: 4216 Good Answers: 194	#2 Re: Rate constant (sulfidation) units 09/08/2009 2:42 PM
	Hi markmai86, Looks to me like they have thrown in pressure; Corrosion units are g/(cm²)(s). If you divide this by pressure units (g_f/cm²), you get (g)(g_f)/(cm⁴)(s). Does that make sense? Mike __________________ "Reason is not automatic. Those who deny it cannot be conquered by it. Do not count on them. Leave them alone." - Ayn Rand
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markmai86 (1); Mikerho (1); Milo (1)

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