volume change on mixing iron and carbon (graphite)

You could look up the density of 0.1 Volume percent carbon in steel and make an educated guess as to the volume change.

Or, you can reason that carbon fits fairly nicely into the interstitial sites of pure iron and therefore the net volume change is _________ than the sum of the two initial volumes.

Jim

Thanks Jim! Thats a pretty good idea

-Scott

aSkeptic keeps coming up with these hard homework questions. They might be good exam questions too.

Prof. K

First divide the specified volumes by the elements molar volumes - this will give you the moles of C and Fe. If you want to work off the mass phase diagram, you would multiply the mole numbers by the atomic weights - this gives you grams of C and Fe. Now consult the phase diagram. If the composition falls within the alpha iron field, then the volume of the Fe,C alloy might be findable in tables, but because C is an interstitial solute in iron the volume change will likely be small. If the composition falls outside the alpha iron solubility field, then the saturated alpha iron will be in equilibrium with Fe3C, cementite. Now the volumetrics get dicey for cementite has its own molar volume which is different from that of saturated alpha iron. It has been some 40 years since I last thought about this kind of problem, so I probably omitted some details that ahve escaped my memory.