Ferrite, Austenite, Martensite and more By Mete

It is probably a waste of time, but I keep trying Fe3C structure to the preferred layering present in pearlite. Each unit cell will have a net (minimum) 2+ charge. If this is 3 Fe atoms in a plane sharing 1/2 of two C atoms perpendicular to that plane, which also link to other Fe occupied planes parallel to the first one with the C atoms also sharing adjoining Fe atoms, a sheet structure can be built that is infinite if the Fe plane. I am not chemist enough to completely understand the coordination numbers and geometry. As a geologist I can see the structure much better in my mind than I perceive the chemistry.
 
Shgeo,

Crystallographically (and otherwise) how can you contemplate a unit cell that is not neutral???

That makes the stuff on Star-Trek seem like child's play;) How did you get a positive charge from combining neutral elements anyway?

Remember stable ferrites have a very low gross carbon percentage. The stability of the entire lattice and how much it is pertubed by the additon of other elements is very important, or more carbon would be present in actual materials.

This stuff is immensly complicated, and that's why people like Mete who actually have to do something tangible, like produce a real piece of metal, often skin the cat from the other end. :) One of my points was that a useful and quite similar model can be acheived by coming from the other direction.

That's why band theory was invented from consideration of solids comprised from one type of atom, and then extrapolated to other more complicated materials.

There is a mathematically defined number of crystallograpic group symmetries like the Platonic solids are defined, and the nuclei of any crystalline structure must fit one of them whether comprised of ions, or an array of covalently bound molecules or a single infinite molecule as in a metal. The structure of minerals is largely a descriptive science, and is based upon a body of empirical knowledge tempered by the constraints of the mathematically defined crystallographic symmetries I think. The structure of a mineral is not derivable like the hydrogen atomic orbitals (which includes besides s orbitals ,p d,f, etc, the latter are just very energetically excited hydrogen), at least at this time. Not a slam, just the way things are. Indeed anything beyone the H2+ atom is an extension and approximation but at the same time subject to rigid rules.

Closed shell ions are like stacking pool balls, the symmetry is spherical, and there are no molecular orbitals. A single transition metal ion in an octahedral coordination environment is quite another matter. Spatial distribution of potentially bonding, anti-bonding and non-bonding orbitals is quantized for anything except s orbitals. And linear combinations of the the s, p, d, f, orbitals can be made to maximize spatial quantization in a particular symmetry. Attempting to model that and at the same time construct an infintely repeating giant molecule that fits one of the permitted cyrstallographic symmetry groups (i.e a metal or mtalloid) is a b*tch. If your making an infinte molecule, you have to know where the electrons are. Electrons define molecules. That's just too hard. Hence, band theory.

Maybe this is all babble, if so my apologies. I just hated to see folks like jhiggens abandon stuff that they knew...it's a valid way to look at things, just in this case a very difficult way most of the time. But not always--think of the metal as one giant repeating molecule and it does work for some things.

Sorta like is an electron a wave or a particle? Sometimes one perspective works better than another--it was reasonable to ask what is a Fe-C bond like in ferrite for for example.

Further appologies to the the guys that just want to make better knives. I guess the take-home is things are complicated and people don't understand everything...but you knew that already.:)
 
The sad thing is that Fe3C is not stable , it is what we call metastable, that is partly stable . The stable form of carbon in steel is graphite.
 
"The sad thing is that Fe3C is not stable , it is what we call metastable, that is partly stable . The stable form of carbon in steel is graphite."

Mete, like I'm trying to say, it's those damned electrons finding the lowest energy on their own! They know more than we do, no matter what end of the cat we start at. And you usually can't see the buggers with crystallograhy.;)

For shgeo, in a nutshell, you started with n carbon atoms, say a piece of neutral graphite or diamond. And 3n iron atoms say a bigger chunk of iron, also neutral. Mix them together, metastable or not and it should be neutral. However you're producing this model, you lost a bunch of electrons somewhere. Something is very wrong!

Maybe you're pushing some computer program beyond it's capabilities?
 
but how many electrons will make my knives shine more:confused: :D
if I use the cat fur
I think I'd be farther ahead but which end of the cat will work better.. ;)
:D
mete I got your package yesterday :)
 
Firkin,
It's not a computer program, its my long ago classes on crystal chemistry. The Fe3C is just the base formula that I took as a simple way to think of carbides. I know that this is just the simplest form of carbide structure-at least that I have seen referenced and was trying to work out a mental model for the layered pearlite structure. I haven't seen any formula for metal carbides that appears charge balanced as they all have excess + charges for C----, so there must be a role for alloying elements or a different chemistry. My perception now is that the C is at least partially covalently bonded to the Fe, the Fe-partially at least, metallic bonded and the whole structure available as a (quasi?) cation (++?). I am assuming C---- and Fe++ for valence states.

I probably should give this up while I am not too far behind in my understanding...

Graymaker-undoubtedly the south end of one northbound feline, otherwise known at the cat's a**.
 
Shgeo, I started another thread called "ferrite structure", if you're interested. No need to keep cluttering up this one.

Graymaker,

From some of the catfood I've smelled, either end of the cat may be just as stinky!:barf:


Edit: Sorry Shgeo, got delayed. posting it now.
 
tuna is less money than most of it too:) The cat's A$$
may not be the best end , it may smear the polish :eek: :)
 
ok, boys hold on just a minute.
#1 a molecule is made up of two or more atoms.
#2 many elements are metals even though we may think of them otherwise. examples hydrogen, sodium, and calcium.
#3 iron carbide is a compound consisting of iron and carbon.
#4 what we think of as steel is a mixture of elements and compounds in solution. it just happens to be a solid at room temp.
#5 many substances are crystalline in nature as solids

these items are characteristics and not mutually exclusive or dependant. each element or compound has its own characteristics and it follows its own rules accordingly.
 
steelfirebug,

I admit we were getting off on a tangent but in answer to your comments above:

1. Yes, atoms that bond together form molecules. In a true metallic bond, the atoms are packed as close as they can get and share their valence electrons, This is why they are such good conductors of heat and electricity- there is little resistance to flow of electrons. Viewed this way, the whole piece of metal is like a super molecule.

2. Yes the alkalai and alkalai earth metals in the first two columns of the Periodic Table are technically metals. They do not form metallic bonds at what we think of as standard temperature and pressure conditions. Hydrogen, for instance, may form a metal at extreme pressures in the depths of Jupiter's atmosphere. Na, K, Ca and Mg (and also the other less common members of the two left hand columns of the periodic table) can be made into metals, but they are very unstable and will burn with ease. They are most suited to form ionic bonds rather than metallic.

3. No one is arguing about wether Fe3C is a compound. the discussion is over how the stuff is bonded.

4, Yes, steel, especially if it has more than 0.85 % C, forms a solid solution of Fe, C and other alloying elements.

5. Except for quenched molten material (technically glass),all naturally occurring, inorganic solid materials are crystalline.
 
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