Re: cif files for austenite

2008-11-03 Thread miguelhg

Hi Antonio
I have tried the position of C atom, and  i have supposed that could be in
8a,whic is an intersticial position, as Frank says,  but you have to
specify the site occupation, which is related to carbon content.
Best wishes.
Miguel Hesiquio
On Fri, October 31, 2008 8:05 am, Frank Girgsdies wrote:
 Dear Antonio,


 as far as I know, austenite is just a solid solution of a few mole-% of
 carbon in gamma-iron. Thus, you essentially need the structure of
 gamma-Fe, which is very simple, as it is an fcc metal (space group Fm-3m, a
 = 3.6468 A, just one
 Fe atom located on 0,0,0).
 I found one ICSD entry for austenite.
 However, the dissolved carbon is placed sharing
 the Fe site in this structure, which I doubt makes sense from the chemical
 point of view. I would bet the carbon atoms are actually located
 on interstitial sites instead. Anyway, as we are talking about a few MOLE-%
  of carbon here, and carbon is much lighter than iron, I think neglecting
 the carbon will not make much of a difference (both for the accuracy of the
 calculated relative intensities and the quantification in wt-%. Thus, I
 would just use gamma-Fe as a replacement for austenite here.

 Cheers,
 Frank


 --
 Frank Girgsdies
 Department of Inorganic Chemistry
 Fritz Haber Institute (Max Planck Society)
 --


 antonio josé wrote:
 Dear All.




 I trying analyze phases in a steel sample using   X-Ray technique. The
 analysis of X-Ray pattern shows that the main phases are ferrite and
 austenite. The next step would be quantify these phases by Rietveld
 method using TOPAS 3.0. I am looking for cif files for austenite and I
 didn’t find it in WEB free database or in ICSD database.

 Do anyone has this cif file or could tell me where I can find?




 Thanks a lot,


 Antonio José


 [EMAIL PROTECTED]








Re: cif files for austenite

2008-11-01 Thread Alan Hewat
 I am looking for cif files for austenite and I
 didn’t find it in WEB free database or in ICSD database.

Frank is quite correct here. Austenite is gamma-iron, which you can find
immediately with Google or Wikipedia:
http://en.wikipedia.org/wiki/Austenite

Small amounts of carbon or hydrogen dissolved in gamma-iron, as reported
in ICSD, is not going to change the X-ray pattern, since Fe-scattering
will dominate. ICSD only reports what people publish. I believe the 1970
X-ray paper on austenite listed in ICSD only reports the lattice
constants, and doesn't actually claim to locate the carbon.

Alan.
__
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
[EMAIL PROTECTED] +33.476.98.41.68
  http://www.NeutronOptics.com/hewat
__



Re: cif files for austenite

2008-11-01 Thread Alan Hewat
 The next step would be quantify these phases by Rietveld method using
TOPAS 3.0.

BTW, it shouldn't need a sophisticated Rietveld refinement to distinguish
between the relative quantities of simple FCC and BCC compounds - some
peaks may overlap almost completely, but others not at all.

I worry that people rely so much on databases and computer programmes, and
so little on thinking.

Alan.
__
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
[EMAIL PROTECTED] +33.476.98.41.68
  http://www.NeutronOptics.com/hewat
__



Re: cif files for austenite

2008-10-31 Thread Frank Girgsdies

Dear Antonio,

as far as I know, austenite is just a solid solution
of a few mole-% of carbon in gamma-iron.
Thus, you essentially need the structure of gamma-Fe,
which is very simple, as it is an fcc metal
(space group Fm-3m, a = 3.6468 A, just one
Fe atom located on 0,0,0).
I found one ICSD entry for austenite.
However, the dissolved carbon is placed sharing
the Fe site in this structure, which I doubt makes
sense from the chemical point of view.
I would bet the carbon atoms are actually located
on interstitial sites instead.
Anyway, as we are talking about a few MOLE-%
of carbon here, and carbon is much lighter than
iron, I think neglecting the carbon will not
make much of a difference (both for the accuracy
of the calculated relative intensities and
the quantification in wt-%.
Thus, I would just use gamma-Fe as a replacement
for austenite here.

Cheers,
Frank

--
Frank Girgsdies
Department of Inorganic Chemistry
Fritz Haber Institute (Max Planck Society)
--

antonio josé wrote:

Dear All.

 

I trying analyze phases in a steel sample using   X-Ray technique. The 
analysis of X-Ray pattern shows that the main phases are ferrite and 
austenite. The next step would be quantify these phases by Rietveld 
method using TOPAS 3.0. I am looking for cif files for austenite and I 
didn’t find it in WEB free database or in ICSD database.


Do anyone has this cif file or could tell me where I can find?

 


Thanks a lot,

Antonio José

[EMAIL PROTECTED]