Another little nugget of information to chew on. My other half (who just happens to be a cement chemist and the reason I've worked on this 'orrible stuff!) tells me that most cement kilns have moved to forced air cooling of the clinker these days - one of the effects apparently is a reduced setting time - any guesses as to why this might be? :-) Pam
________________________________ From: Reinhard Kleeberg [mailto:[EMAIL PROTECTED] Sent: Fri 30/05/2008 5:36 AM To: rietveld_l@ill.fr Subject: Re: RES: ADS Hi Lubo, the difference between 6 and 7 % MgO is bigger than 15 % relatively, thus the error by wrong re-scaling (e.g. if 10 % "amorphous" are missing) is smaller than the error discussed. And, if the "true" content of periclase should be about 5 %, than a measured value of 7 % is worth to be discussed to be a real systematic error. This is an over-estimation by 40 %. In the very past (30 years and more ago) people who applied single line methods carefully have been able to determine "simple" phases like free lime, quartz, anatase in low concentrations very accurate (of course after optimizing their technique), and I believe that such methods are still in use in routine product control. So I feel it is worth to think about why a Rietveld refinement should perform worse. I agree with you that the cement business is full of dubious advertisement for machines and methods for accurate QPA. But this is not a reason to finish thinking about how to improve QPA methods. Best Reinhard Lubomir Smrcok schrieb: > Hi, > I really wonder why do you bother about 1% difference when the error > of the method (XRD, quantitative phase analysis) could reach 10% > (absolute) ... > People in the discussions appearing here seem to forget about two things: > > i) "quantitative" phase analysis done by rietveld method is always > re-scaled to 100%, i.e. the accuracy of % attributed to the individual > phase directly depend on %'s attributed to the another phases present > in the mixture (i.e. when you forget or ignore one phase having 10% > share, those %'s are redistributed among the other phases); > > ii) this method completely ignores any amorphous parts (i.e. those not > providing Bragg peaks, to be more exact) - ignores, because it cannot > do anything else about it. Obviously, when you compare XRF and XRD you > can find yourself in troubles as XRF dos not bother about the state of > the compounds. > > Finally, my personal advice. If someone tells you you can analyze > clinkers or even cements by XRD accurately, do not trust him. He, most > probably, thinks of selling you a machine you can hardly use for this > purpose :-) > Bad luck if you have already bought it ... > > Best, > Lubo > > > > On Thu, 29 May 2008, [iso-8859-1] José Carlos Cordeiro wrote: > >> My samples are cements (fine samples with 30 microns) and don't need >> micronize its. The problem in my refinements is that periclase >> quantified with fixed slit is bigger than MgO by Fluorescence, and >> its impossible. Ex: >> >> >> >> Periclase with fixed slit: 7,14% >> >> MgO by XRF = 6,84% >> >> >> >> We know that part of MgO (1,5-2,0%) go to the structure of C3S an C2S >> phases, so periclase expected in this sample is 4,8% - 5,3%. If we >> consider this, the errors of refinement is not very slim. >> >> >> >> Sorry for my bad English!!! >> >> >> >> regards >> >> >> >> =========================================== >> >> José Carlos Cordeiro >> >> Diretoria Técnica - Laboratório Central >> >> Centro Técnico - Curitiba >> >> Rodovia PR-092, 1303, Abranches, 82130-570 Curitiba-PR >> >> Votorantim Cimentos >> >> [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> >> >> www.votorantimcimentos.com.br >> >> Fone: + 55 041 3355-1380 >> >> Fax: + 55 041 3355-1358 >> >> =========================================== >> >> -----Mensagem original----- >> De: Whitfield, Pamela [mailto:[EMAIL PROTECTED] >> Enviada em: quinta-feira, 29 de maio de 2008 17:40 >> Para: José Carlos Cordeiro; rietveld_l@ill.fr >> Cc: Mitchell, Lyndon >> Assunto: RE: ADS >> >> >> >> Hi Jose >> >> >> >> Errors in the region of 1wt% aren't unheard of in complex mixtures >> (and the liklihood of the second decimal place being meaningful is >> very slim). However there are other possible explanations and one in >> particular comes to mind. >> >> Did you micronize your sample? If yes then feel free to ignore the >> following! If not then it might be worth thinking about. >> >> >> >> We did a systematic study on the effect of particle statistics on the >> repeatability of quantitative analysis on one of the NIST cements >> last year (presented at the ICCC in Montreal - should really go >> somewhere more accessible). We compared different divergence slits, >> micronized and unmicronized samples, spun and static, and >> remounted/repeated the experiments 3 times each for real statistics >> as opposed to esds. >> >> >> >> Funnily enough the phase that showed the biggest anomaly in one of >> the unground sample was the periclase - obviously a big (by XRD >> standards) lump fell into the sample from the kiln that made up the >> NIST batch and made it through the mill at the plant. Without >> grinding it we got 0.1, 0.1 and 2wt% one series of 3, versus 0.6, 0.6 >> and 0.6 wt% (this is from memory so don't don't quote me!) for the >> micronized sample. >> >> This was the result that we should have got theoretically but it was >> nice to see it work in practice, and the periclase did such a nice >> job for us by sticking out like a sore thumb even without a Rietveld >> analysis! BTW there was no statistically significant difference (95% >> limits) in the results of the C3S and C2S phases between ground and >> unground samples - mostly because the errors in the unground samples >> were so large! The minor phases were another matter. In the >> micronized samples the choice of divergence slit size made little >> difference, but with the unground samples they made a significant >> difference. >> >> >> >> To cut a long story short it all comes down to particle statistics - >> with an ideal powder the choice of fixed versus variable slits (or >> even different fixed slits) should make no difference (assuming that >> the Rietveld software can handle the difference in profiles). Moral >> of the story - sample prep, sample prep and more sample prep! >> >> >> >> Pam >> >> -----Original Message----- >> From: José Carlos Cordeiro [mailto:[EMAIL PROTECTED] >> Sent: May 29, 2008 3:53 PM >> To: rietveld_l@ill.fr >> Subject: ADS >> >> I have a Programmable Divergence Slit (incident beam) in my >> difratctometer, that can work in automatic mode (irradiated length) >> or fixed mode (0.5 degree or 1.0 degree etc). What is the best >> collect mode for Rietveld Refinament?? >> >> >> >> I did refinement two difractograms collected in booth >> configuration (fixed 0.5 degree and automatic mode), the results in >> the fase "Periclase" (cement fase) changed, see below: >> >> >> >> Periclase with 0.5 degree = 6.08% >> >> Periclase wich automatic mode = 7.14% >> >> >> >> Note.: The refinement of the difractograms collected with >> automatic mode went converted to fixed mode by software. >> >> >> >> >> >> >> >> What do you think about this? >> >> >> >> regards >> >> >> >> =========================================== >> >> José Carlos Cordeiro >> >> Diretoria Técnica - Laboratório Central >> >> Centro Técnico - Curitiba >> >> Rodovia PR-092, 1303, Abranches, 82130-570 Curitiba-PR >> >> Votorantim Cimentos >> >> [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> >> >> www.votorantimcimentos.com.br >> >> Fone: + 55 041 3355-1380 >> >> Fax: + 55 041 3355-1358 >> >> =========================================== >> >> >> >>
