Chemical Structures of metals.

[GutZ]

I should know this really for the field I am in but since I am still a student, and we don't really cover it well, I have a question.

 

Take Steel (Iron/Carbon),

 

When it's brought to a temperature of "A" or so it changes phase. What phase, doesn't really matter I just know that at certian phases the structure of the metal atoms changes from like BCC, FCC and HCP to another. I was wondering what sets those states? Like is it an specfic energy level where the structure changes to HCP, or whatever?

 

I am not making sense probably but I am sure one of you will get it.

[YT2095]

those are Crystaline stuctures you`re talking about, not atoms, atoms stay the same.

as for phases there are only 5 that we know of anyway, Solid, Liquid, Gas, Plasma, Bose Einstein condensate. in chem we deal only with the 1`st 3 mostly.

so "Phase" isn`t the correct wording either.

 

using this data, can you re-define your question again please?

[GutZ]

No. Well I should of said Iron sorry. I had steel on the mind.

 

http://en.wikipedia.org/wiki/Ferrite_%28iron%29

 

In pure iron, ferrite is stable below 910°C. Above this temperature the face-centered cubic form of iron, austenite (gamma-iron) is stable. Above 1390°C, up to the melting point at 1534°C, the body-centred cubic crystal structure is again the more stable form (delta-iron).

 

 

Structure

FCC-->BCC

 

Phase

Austentite--->Delta Iron (eek)

 

I guess the Phase is irrelvant...I just want to know what causes a cystalline structure to change.

[Tetrahedrite]

I think I know what you are trying to ask, and the answer (nearly always) has to do with thermodynamics. The iron will always react so that it has the lowest possible energy. When you heat iron (or it's alloys) up to certain temperatures, it will rearrange itself to give a lower lattice energy. If it did not do this, it would not be in thermodynamic equilibrium.

 

To put it another way....... You'll probably find that the reaction from from BCC iron to FCC iron is endothermic, and when you heat the system up, it reacts in such a way to try and counteract that heat (stress) ie it reacts in the endothermic direction, BCC to FCC. This is not at all dis-similar to Le Chatelier's principle.

[psynapse]

^Good answer, IMO.

[GutZ]

Yeah that's it, perfect! thank you. Thermodynamics...*shudders*, I guess I should read into that.

[Tetrahedrite]

Yeah that's it, perfect! thank you. Thermodynamics...*shudders*, I guess I should read into that.

No problem. Thermodynamics is the fundamental driving force behind all chemistry so it really is a good thing to learn, even in a basic sense.

[insane_alien]

yeah thermodynamics is pretty important. even if its as boring as hell. and i mean reallly BORING. on a side note, guess what class i'm in just now

[jdurg]

Yes, but thermodynamics classes typically have the most interesting and exciting demos.

[GutZ]

I want to get as much information as I can now, being a Metal Casting Technician (glorified titles ) , and wanting to advance my education later, it will help me make that leap when I get the money or assistance to do it.

 

Plus...it impress people

 

Thermodynamics is interesting for me, it's just like, they purposely find the most boring way to present it (well in books anyway).

[insane_alien]

do you want to go to my thermo lectures then?

[GutZ]

Do I have to take notes for you?

[insane_alien]

yes and the must be surrounded by a border of amusing doodles as they would be if i was taking notes.