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.


 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


RE: UVW - how to avoid negative widths?

2009-03-20 Thread miguelhg
Hi to all!,
in fact, the Cagliti's expression is just a way to show the angular
variation of fwhm, as was mentioned was usef for neutron diffraction and
adopted in XRD, we can also build another dependence such as  FWMH vs
2theta directly and  it is useful to evaluate size and strain, the problem
is that many refinement codes have the FWMH angular dependence in terms of
Caglioti's equation. By the way, how can I get the paper of Young and
Desai?,because I have tried a search in the web,but i did'nt find the
best regards.

Miguel Hesiquio

Miguel Hesiquio-Garduño
Profesor Titular A
Departamento de Ciencia de Materiales
Academia de Ciencias de la Ingeniería
ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011

On Thu, March 19, 2009 5:22 pm, wrote:
 From what I've read of Cagliotti's paper, the V term should always be
 negative; or am I reading it wrong?

 Additionally, there is some good work on the use of the Cagliotti (and
 TCHZ) functions in the paper by Young and Desai; it also goes over how to
 incorporate sample dependent terms into the expression.

 Young, R. A.  Desai, P. 1989, 'Crystallite Size and Microstrain
 Indicators in Rietveld Refinement', Archiwum Nauki o Materialach, vol.
 10, no. 1-2, pp. 71-90.

 Alan Hewat wrote:

  if you have access to the refinement code.

 This is why I love Topas. All of the the code used in the refinements is
 there for you to see!  :)



 Matthew Rowles

 CSIRO Minerals
 Box 312
 Clayton South, Victoria

 Ph: +61 3 9545 8892
 Fax: +61 3 9562 8919 (site)