http://journals.iucr.org/j/issues/2001/02/00/ks0032/ks0032.pdf <http://journals.iucr.org/j/issues/2001/02/00/ks0032/ks0032.pdf> is the paper she referenced.
Cheers Matthew ________________ Matthew Rowles CSIRO Minerals - Clayton Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] _____ From: Madsen, Ian (Minerals, Clayton) Sent: Wednesday, 3 October 2007 10:41 To: rietveld_l@ill.fr Subject: RE: Density calculations for amorphous products Dear Maria, We are also working on methods for determination of amorphous material. Can you please send me the full reference to the paper you quoted in your message. I urge great caution in the application of the Brindley model for correction of your QPA. Since the microabsorption correction is based on (MU - MUaverage)*R where MU is the linear absorption coefficient (LAC) of the phase and MU average is the LAC of the mixture and R is the particle radius. In your case MU and MUaverage should be the same (due to having the same/similar chemistry) and only differ because of packing density. Any difference in particle size may induce some microabsorption issues, but estimation of the correct value of R is problematic at best. The recent round robin on quantitative phase analysis highlighted the fact that while microabsorption is the greatest impediment to accuracy in QPA, misuse of the Brindley model frequently served to degrade, rather than improve, accuracy. Cheers o----------------------oo0oo---------------------------o Ian Madsen Team Leader - Diffraction Science CSIRO Minerals Box 312 Clayton South 3169 Victoria AUSTRALIA Phone +61 3 9545 8785 direct +61 3 9545 8500 switch +61 (0) 417 554 935 mobile FAX +61 3 9562 8919 Email [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> o----------------------oo0oo---------------------------o -----Original Message----- From: Fabra-Puchol, Maria [mailto:[EMAIL PROTECTED] Sent: Tuesday, 2 October 2007 7:46 PM To: rietveld_l@ill.fr Subject: Density calculations for amorphous products Hi all, I have a question concerning density calculations, I'm actually working on an amorphous phase quantification method using Rietveld and most part of the samples I'm working with contain high quantity of silica (amorphous and crystalline). I've attentively read the paper: "Determination of the crystallized fractions of a largely amorphous multiphase material by the Rietveld method" (X. Orlhac, C. Fillet,...) and I found out that the Brindley correction can be applied in my case. When I calculate the linear absorption coefficient of each phase I must to take into account also the amorphous phase, isn't it? . I just would like to know if someone could indicate me how to calculate this factor making difference between an amorphous and a crystalline phase (for example, concerning silica). I know the atomic absorption coefficient of each element must be multiplied by the packaging density in the case of powders but it just talks about the crystalline phases, what about the amorphous phase? Thanks for your help Sincerely, Maria Fabra Puchol Responsable Laboratoire Structures Structural Laboratory Manager ------------------------------------- Saint-Gobain CREE 550 Avenue Alphonse Jauffret BP224 84306 Cavaillon Cedex - France tel: 00 33 4 32 5 09 36 fax: 00 33 4 32 50 08 51 e-mail: [EMAIL PROTECTED]