I don't remember saying that reflection would work well with wollastonite only that a capillary won't get rid of the orientation (or at least that was my intention). As always this is going to vary from sample to sample, i.e. how large the particles are, aspect ratio of the particles, the diameter of the capillary, pure or mixture, etc. Orientation with needles is going to be more of a problem in a 0.3mm versus a 0.8mm capillary. Particle statistics are also a potential issue with samples like this. If they are large enough to orientate badly then the crystallites are probably large and the capillary will do a better job with the statistics The MD correction doesn't work very well for alot of these systems, SH is better as long as the correlations don't get out of hand (which they can quite easily). However 0.9 is still significantly orientated so it doesn't get rid of it by any means. With platey particles you can pretty much eliminate the preferential orientation with a capillary versus flat plate with significant impact of quantitative analysis results (paper published in Powder Diffraction a couple of years ago). I do have reflection data from 400 mesh wollastonite (albeit with MoKa from a high pressure gas cell) which can be fitted quite nicely with SH (lousy with MD). The quantitative analysis results from the carbonation are good enough to extract a rate constant which suits me nicely. The additional penetration of the MoKa should help with the stats in this case even if transparency becomes a problem - you can't win eh? Unfortunately it's quite difficult to completely decouple orientation, statistcs and microabsorption as they are all related to size. Pam
________________________________ From: Martin [mailto:[EMAIL PROTECTED] Sent: Fri 16/05/2008 10:04 AM To: Whitfield, Pamela; rietveld_l@ill.fr Subject: RE: Preferred orientation? In fact I think you might find it helps quite a bit. Have a look at: http://img.chem.ucl.ac.uk/www/vickers/po/po.htm Martin ________________________________ Subject: RE: Preferred orientation? Date: Thu, 8 May 2008 10:55:12 -0400 From: [EMAIL PROTECTED] To: rietveld_l@ill.fr I do that myself but it doesn't always help much if you've got something like wollastonite! J From: Martin [mailto:[EMAIL PROTECTED] Sent: May 8, 2008 10:51 AM To: rietveld_l@ill.fr Subject: RE: Preferred orientation? Forget all that long winded stuff. Just collect the data on capillary transmission geometry and avoid all (well, most of) the fuss. Martin Vickers ________________________________ Get fish-slapping on Messenger! Play Now <http://clk.atdmt.com/UKM/go/msnnkmgl0010000008ukm/direct/01/> ________________________________ Get fish-slapping on Messenger! Play Now <http://clk.atdmt.com/UKM/go/msnnkmgl0010000008ukm/direct/01/>
