Hello Rory, Ian, and the rest. I've been planning to do a similar calibration for a long time for our Anton Paar HTK1200N but I've had to postpone it over and over again. The approach by John Evans is very intriguing to me, but I'm lacking a recent Topas version and I'm not sure if very old 2.1 will do it.
However, I think that a way to circumvent the simultanious refinement of temperature shift and wrong height is to use parallel beam if you have the possibility. On one hand you could first determine the temperature behaviour as the peaks shouldn't really shift because of the wrong height when using parallel beam. When the temperature behaviour is known, change back to focusing geometry and calibrate the height. On the other hand it might be possible to get the correct height in different temperatures just by changing the sample holder position until it halves the direct beam intensity. This is possible at least for our ceramic sample holder, I'm not sure how this would work with Pt-strip in other ovens. I'm very interested about suitable test materials. I was planning to go with corundum and parallel beam first, but now that this thread is open, I'll wait a bit longer (again). Regarding the calibration with phase change temperature, Robert Dinnebier has some materials listed on his webpage: http://www.fkf.mpg.de/xray/html/temperature_calibration.html Please correct me if I've made much mistakes above, I'm still at rather beginning of my learning curve :-) Cheers, Mikko ian.mad...@csiro.au wrote: > Hi Rory, > > At the moment we are in the same position i.e. attempting to calibrate the > temperature and systematic offsets in an HTK10 furnace with Pt strip heater. > One approach is to take materials which have a well defined solid-solid phase > transition or melting point and observe this as a function of set > temperature. Unfortunately, most materials only provide one or two > calibration points and hence you will need to heat several samples in order > to cover a wide temperature range. > > At the moment we (and by "we" I mean my PhD student Mark Styles is doing all > the work and I stick my head in occasionally and say "how's it going?") have > taken an 'external standard' approach (we cannot add a standard to our sample > and risk reaction). In this we heat a material with known thermal coefficient > of expansion (TCE), measure the unit cell edge a function of temperature and > then determine a calibration curve. However, the flaw in this approach will > be the impact of other systematic errors (e.g. sample displacement) on the > observed peak positions and hence cell edge. > > John Evans (Durham Uni) uses a modified TCE approach in which he adds two > standards with different TCE's (I haven't got the references to hand, but > this is described in one of his papers) and normalises observed cell edge (or > cell volume) to that at the starting temperature (To). Instead of using the > absolute cell edge (volume) for each phase, he then uses the difference > between the two compounds as a way of eliminating the systematic errors which > should affect both equally. > > If you pardon the pun, this is a hot topic for us at the moment - we are > coming up to some synchrotron time where T calibration will be important - we > have not completely sorted out the fine details but intend to:- > > (1) Use a mixture of NIST silicon and corundum > (2) Heat to various temperatures over the range of interest > (3) Use the 'surface analysis' approach (Stinton and Evans) which relies on > use of the Topas Rietveld software. In this, the cell edge is not refined, > but defined as a function of applied temperature, the temperature offset (a > refinable parameter) and the published TCE equations for each phase. > > What we hope to end up with is an analytical method which is quick and easy > to apply to produce a T calibration for every new heater - i.e. it should not > be an onerous task so that it can be carried out frequently. > > I hope this helps - we still have much fine detail to sort out. > > 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 ian.mad...@csiro.au > o----------------------oo0oo---------------------------o > > -----Original Message----- > From: r.m.wil...@qmul.ac.uk [mailto:r.m.wil...@qmul.ac.uk] > Sent: Thursday, 8 October 2009 3:14 AM > To: rietveld_l@ill.fr > Subject: HT XRD calibration > > > Dear All > We have an Anton Paar HTK16 furnace with a Pt strip. I am > hoping to calibrate it both thermally and mechanically (height shift) > using either alpha alumina or ceria so as to better identify HT > phases. Have any of you experience of this, or better suggestions for > calibrants? My only serious worry is whether there is any potential > for ceria to react with, the Pt strip? > (Perhaps under vacuum?) I'd welcome any advice or suggestions. > Yours > Rory > > ************************************ > Dr R.M. Wilson, > Experimental Officer & RPS > School of Eng. and Materials, > G27 & G30 X-ray Laboratories, > Francis Bancroft Building > Queen Mary College > University of London > Mile End Road > LONDON E1 4NS > UK > Tel: +44 (0)20 7882 7938 > Fax: +44 (0)20 7882 7931 > ************************************ > > > -- Mikko Heikkilä, M.Sc. Laboratory of Inorganic Chemistry Department of Chemistry P.O.Box 55 (A.I. Virtasen aukio 1) FI-00014 University of Helsinki phone: +358 9 191 50216 fax: +358 9 191 50198 mobile: +358 440 572 372 email: mikko.j.heikk...@helsinki.fi
