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 ************************************