Re: wt% to volume percent
I think that if you have normalised wt% (or you're sure that all phases are identified and you get a total of 100 wt%) then you can divide each wt% by the phase density and renormalise. If you have an unidentified phase then it is not really practicable as you would have to estimate (or guess in the worst case) it's density before using the above method, leading to unknowable error margins. I think the above is correct. I remember looking at this problem once to try rationalising XRD and thin section point-counting data, but that was many years ago. Best Regards, Mike Andrews. Subject:wt% to volume percent To: rietveld_l@ill.fr From: Mr. Tony Raftery [EMAIL PROTECTED] Guys, can anyone send me description (or reference) for the conversion of weight percent to volume percent for a (solid) mixture - volume percent is favored by metallurgists (and others). thanks in advance, Tony Raftery Tony Raftery Senior Technologist AEMF XAF, R Block Faculty of Science, GP Queensland University of Technology c/- AEMF, R Block Gardens Point Road, Brisbane, 4000 (or) GPO Box 2434 Brisbane 4001 AUSTRALIA ph+61 7 3138 2271 fax +61 7 3138 5100 [EMAIL PROTECTED] http://www.xaf.qut.edu.au/ please note new phone number from 16/10/2006 - X-Ray, SEM, IT Support, Image Analysis Room 9, Geoscience Building, School of Human and Enviromental Sciences, The University of Reading, UK. Tel: +44(0)118 378 7974 -
Re: wt% to volume percent
Dear Tony, diffraction intensity are sensible to volume fractions, not weight percent. What you see in the Rietveld formulas are weight fractions because they convert the scale parameter (in which there is the volume fraction) into weight fractions using the density (the ZMV factor containing number of molecules, molecular weight and cell volume, a way to get the density taking into account the scale factor contains also a squared cell volume at the denominator). So to get volume fraction it's more easy as you only do: vol % phase i = (scale factor phase i) / Sum(all phases scale factors) no density involved. Best regards, Luca Lutterotti On Mar 10, 2007, at 11:52 PM, Mr. Tony Raftery wrote: Guys, can anyone send me description (or reference) for the conversion of weight percent to volume percent for a (solid) mixture - volume percent is favored by metallurgists (and others). thanks in advance, Tony Raftery Tony Raftery Senior Technologist AEMF XAF, R Block Faculty of Science, GP Queensland University of Technology c/- AEMF, R Block Gardens Point Road, Brisbane, 4000 (or) GPO Box 2434 Brisbane 4001 AUSTRALIA ph +61 7 3138 2271 fax +61 7 3138 5100 email [EMAIL PROTECTED] http://www.xaf.qut.edu.au/ please note new phone number from 16/10/2006
N-TOF
Dear all: We're in the midst of Rietveld refinements of neutron TOF data acquired at LANSCE NPDF. The NPDF gives very high backgrounds in low d- values (TOF time), which drop quickly with d-value. After many iterations, the fit between the data and model looks very reasonable, including the background. The model is very close to what has been reported before and it makes sense. However, the Chi^2 doesn't come down close to one. We refined using the Le Bail method, and got a very similar result, including the Chi^2 value (about 20). We feel comfortable with our model, but a high Chi^2 is bothering. Reading the literature, high Chi^2 can occur where data are collected to very high precision. We think this might be our case, but how can we prove so? Any comments and suggestions are appreciated. Best, Juske * Juske Horita Chemical Sciences Division, Oak Ridge National Laboratory P.O.Box 2008, MS 6110 Oak Ridge, TN 37831-6110 (865) 576-2750; Fax (865) 574-4961 For express-mail: Juske Horita Chemical Sciences Division, Oak Ridge National Laboratory Bethel Valley Rd, 4500S, S214 Oak Ridge, TN 37830
Problems using TOPAS R (Rietveld refinement)
Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
RE: N-TOF
Juske, One point you should know the background in a TOF powder diffraction pattern is not high - that is a nearly constant background multiplied by a strongly varying incident spectrum which is much higher at short TOF than at long TOF. Do a divide by incident spectrum and you wll see what I mean. Moreover, if you plot delta/sig vs TOF (in POWPLOT - GSAS) the resulting plot should be uniformly noisy as a function of TOF - that assures that the weights properly include the incident spectrum. If not - talk to your instrument scientist. As for your chi**2 question - a high value, assuming the difference curve shows that you have no unsatisfied systematic error, can simply be from counting too long. If the difference curve is OK the structures are chemically sensible, I'd not worry about it (and reviewers shouldn't either). Bob Von Dreele R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Horita, Juske [mailto:[EMAIL PROTECTED] Sent: Monday, March 12, 2007 8:09 AM To: Rietveld_l@ill.fr Subject: N-TOF Dear all: We're in the midst of Rietveld refinements of neutron TOF data acquired at LANSCE NPDF. The NPDF gives very high backgrounds in low d- values (TOF time), which drop quickly with d-value. After many iterations, the fit between the data and model looks very reasonable, including the background. The model is very close to what has been reported before and it makes sense. However, the Chi^2 doesn't come down close to one. We refined using the Le Bail method, and got a very similar result, including the Chi^2 value (about 20). We feel comfortable with our model, but a high Chi^2 is bothering. Reading the literature, high Chi^2 can occur where data are collected to very high precision. We think this might be our case, but how can we prove so? Any comments and suggestions are appreciated. Best, Juske * Juske Horita Chemical Sciences Division, Oak Ridge National Laboratory P.O.Box 2008, MS 6110 Oak Ridge, TN 37831-6110 (865) 576-2750; Fax (865) 574-4961 For express-mail: Juske Horita Chemical Sciences Division, Oak Ridge National Laboratory Bethel Valley Rd, 4500S, S214 Oak Ridge, TN 37830
Re: Problems using TOPAS R (Rietveld refinement)
I think that I just did a good job in my quantification: 50,2% calcite and 49,8% dolomite. Now I´m moving foward to a sinthetic mixture of calcite, dolomite and kaolinite. I have other questin, how can I determine a trustable value to the Full Axial Model?! Especially the these paramters: sample lenght, source lenght and RS lenght?!?! I´m starting to realize that the temperature factors are the key to the refinement! They change the calculated pattern so much!!! From: jilin_zhang_Houston [EMAIL PROTECTED] Reply-To: rietveld_l@ill.fr To: rietveld_l@ill.fr rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 10:39:41 -0600 Leandro : here is an example of calcite I used. You can use min and max to confine the parameters. One way to know whether it is right is to mix a known fraction of a compound, e.g. ZnO with a ratio of original sample/ZnO=100/15. At the end of the refinement, you have N components with N corrected(with volume and density) scalefactor, S(i), Weight(i)=S(i)/S(ZnO)*15 the sum of all weight(i) should be close to 100 if the whole thing is crystalline. str phase_name calcite scale sc_calcite 0.0001813894308 space_group R-3c r_bragg 5.769971925 Crystallite_Size(cs_calcite, 100 min =100; max =1000;) Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite 17.08621648 min =16.9; max =17.1;) site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95 site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9 site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94 PO_Spherical_Harmonics(sh_calcite, 2 ) Cheers J Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d _ Seja um dos primeiros a testar o novo Windows Live Mail Beta- grátis. Acesse http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
