Re : Re : HT XRD calibration
Hi Alex, May be we worked with the same furnace: Inel? I had also the same problem and solved it by making a new sample holder with a smaller thermocouple placed on the side of the sample holder. Patrick Patrick Weisbecker LCTS - Pessac - Message d'origine De : Yokochi, Alexandre alexandre.yoko...@oregonstate.edu À : Rietveld list rietveld_l@ill.fr Envoyé le : Jeu 15 Octobre 2009, 21 h 33 min 31 s Objet : RE: Re : HT XRD calibration Hi all, I've never used one of these Anton Paar furnaces, but with some of my instruments (externally heated, not Pt resistive foil heated) I could actually use the thermocouple as the sample mount. I also had an instrument that had a thermocouple in contact with the powder sample, which due to thermal expansion mismatch would upon heating expand and split the sample surface giving rise to ugly split peaks so be careful... (you can imagine that implementation lasted as many samples as it took me to figure out what the peak splitting problem was). Alex Y Dr. Alexandre (Alex) F. T. Yokochi Assistant Professor Department of Chemical Engineering Oregon State University Corvallis, OR 97331-2702 Voice: (541) 737-9357 Fax: (541) 737-4600 http://oregonstate.edu/~yokochia -Original Message- From: Payzant, E. Andrew [mailto:payza...@ornl.gov] Sent: Thursday, October 15, 2009 6:27 AM To: Rietveld list Subject: Re: Re : HT XRD calibration Patrick, That is a good idea. Note that to actually get rid of the uncertainty you need to be certain that the thermocouple is either reading the temperature of the actual sample volume contributing to the diffraction pattern, or that it is reading the temperature of a location where the temperature is exactly the same as the sample volume. Andrew On 10/14/09 11:25 AM, Patrick Weisbecker weis...@yahoo.fr wrote: Hi, One way to get rid of the temperature uncertainty is to introduce a second thermocouple inside the furnace and to fix it as close as possible from the sample. If the sample is a bulk sample:Drill a hole inside the sample and put the thermocouple inside the hole and if the the sample is made of powder put it inside the powder. The are some miniature thermocouple (0.25-0.5mm diameter), mineral insulated which are unlikely to react with the samples. Patrick - Message d'origine De : Payzant, E. Andrew payza...@ornl.gov À : Mikko Heikkilä mikko.j.heikk...@helsinki.fi Cc : Rietveld list rietveld_l@ill.fr Envoyé le : Mer 14 Octobre 2009, 16 h 39 min 58 s Objet : Re: HT XRD calibration All, The two calibration standard method was described by Andy Drews (Ford Research Lab) in Advances in X-ray Analysis (the proceedings of the Denver X-ray Conference), vol. 44, page 44 (2001). Scott Misture (Alfred Univ), Stephen Skinner (Imperial College), Christian Resch (Anton Paar), and I ran a workshop on non-ambient diffraction at the Denver X-ray Conference in 2008, where we discussed many of these issues. There was a lively discussion with the attendees regarding various experiences with HTXRD, and the difficulty in abtaining the right answer. Too often we are so focused on the precision and accuracy of our refinements that we neglect the temperature issue, to our peril. One issue with the HT16 hot stage is that you will likely need to recalibrate with every new heater strip - don't rely on them behaving the same. Even for a particular strip, use of an internal standard is best if you can use one that does not react with either the strip or the sample. If you push this furnace to temperatures above 1200degC or so, the platinum will creep and the tensioning will change, so that the height/temperature calibration may subsequently be off. I agree fully with the suggestion to use parallel beam optics to eliminate the sample height error. You do lose some angular resolution of course, at least on a laboratory diffractometer, but you take one variable (sample height) out of the refinement. The other BIG problem with the HT16 (and many other non-ambient stages) is knowing the temperature of the SAMPLE (as opposed to the strip). Powders have hopelessly poor thermal conductivity, and the gradients in these furnaces can be substantial. We rarely measure the temperature of the sample directly, and this is another reason why internal standards are very useful - you can use either a known CTE to estimate the delta T over the full temperature range, or a known phase transformation to determine delta T at a single point. I personally prefer the former approach myself. Note that a solid-solid transformation may give a different result than a melting point standard, since the liquid will change the thermal conductivity between the strip and the sample. You can find more discussion of these issues in Mark Rodriguez's chapter in the book Industrial Applications of X-ray Diffraction, or mine
Re: Re : HT XRD calibration
Patrick, That is a good idea. Note that to actually get rid of the uncertainty you need to be certain that the thermocouple is either reading the temperature of the actual sample volume contributing to the diffraction pattern, or that it is reading the temperature of a location where the temperature is exactly the same as the sample volume. Andrew On 10/14/09 11:25 AM, Patrick Weisbecker weis...@yahoo.fr wrote: Hi, One way to get rid of the temperature uncertainty is to introduce a second thermocouple inside the furnace and to fix it as close as possible from the sample. If the sample is a bulk sample:Drill a hole inside the sample and put the thermocouple inside the hole and if the the sample is made of powder put it inside the powder. The are some miniature thermocouple (0.25-0.5mm diameter), mineral insulated which are unlikely to react with the samples. Patrick - Message d'origine De : Payzant, E. Andrew payza...@ornl.gov À : Mikko Heikkilä mikko.j.heikk...@helsinki.fi Cc : Rietveld list rietveld_l@ill.fr Envoyé le : Mer 14 Octobre 2009, 16 h 39 min 58 s Objet : Re: HT XRD calibration All, The two calibration standard method was described by Andy Drews (Ford Research Lab) in Advances in X-ray Analysis (the proceedings of the Denver X-ray Conference), vol. 44, page 44 (2001). Scott Misture (Alfred Univ), Stephen Skinner (Imperial College), Christian Resch (Anton Paar), and I ran a workshop on non-ambient diffraction at the Denver X-ray Conference in 2008, where we discussed many of these issues. There was a lively discussion with the attendees regarding various experiences with HTXRD, and the difficulty in abtaining the right answer. Too often we are so focused on the precision and accuracy of our refinements that we neglect the temperature issue, to our peril. One issue with the HT16 hot stage is that you will likely need to recalibrate with every new heater strip - don't rely on them behaving the same. Even for a particular strip, use of an internal standard is best if you can use one that does not react with either the strip or the sample. If you push this furnace to temperatures above 1200degC or so, the platinum will creep and the tensioning will change, so that the height/temperature calibration may subsequently be off. I agree fully with the suggestion to use parallel beam optics to eliminate the sample height error. You do lose some angular resolution of course, at least on a laboratory diffractometer, but you take one variable (sample height) out of the refinement. The other BIG problem with the HT16 (and many other non-ambient stages) is knowing the temperature of the SAMPLE (as opposed to the strip). Powders have hopelessly poor thermal conductivity, and the gradients in these furnaces can be substantial. We rarely measure the temperature of the sample directly, and this is another reason why internal standards are very useful - you can use either a known CTE to estimate the delta T over the full temperature range, or a known phase transformation to determine delta T at a single point. I personally prefer the former approach myself. Note that a solid-solid transformation may give a different result than a melting point standard, since the liquid will change the thermal conductivity between the strip and the sample. You can find more discussion of these issues in Mark Rodriguez's chapter in the book Industrial Applications of X-ray Diffraction, or mine in Principles and Applications of Powder Diffraction. I chair the non-ambient diffraction subcommittee of the ICDD, and in that capacity I am looking for ways we can develop and standardize these methods. If any of you would like to participate in this exercise please let me know. Perhaps a special issue of Powder Diffraction could be devoted to in-situ high-temperature diffraction papers? Always looking for good ideas... Andrew On 10/8/09 1:40 AM, Mikko Heikkilä mikko.j.heikk...@helsinki.fi wrote: 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
RE: Re : HT XRD calibration
Hi all, I've never used one of these Anton Paar furnaces, but with some of my instruments (externally heated, not Pt resistive foil heated) I could actually use the thermocouple as the sample mount. I also had an instrument that had a thermocouple in contact with the powder sample, which due to thermal expansion mismatch would upon heating expand and split the sample surface giving rise to ugly split peaks so be careful... (you can imagine that implementation lasted as many samples as it took me to figure out what the peak splitting problem was). Alex Y Dr. Alexandre (Alex) F. T. Yokochi Assistant Professor Department of Chemical Engineering Oregon State University Corvallis, OR 97331-2702 Voice: (541) 737-9357 Fax: (541) 737-4600 http://oregonstate.edu/~yokochia -Original Message- From: Payzant, E. Andrew [mailto:payza...@ornl.gov] Sent: Thursday, October 15, 2009 6:27 AM To: Rietveld list Subject: Re: Re : HT XRD calibration Patrick, That is a good idea. Note that to actually get rid of the uncertainty you need to be certain that the thermocouple is either reading the temperature of the actual sample volume contributing to the diffraction pattern, or that it is reading the temperature of a location where the temperature is exactly the same as the sample volume. Andrew On 10/14/09 11:25 AM, Patrick Weisbecker weis...@yahoo.fr wrote: Hi, One way to get rid of the temperature uncertainty is to introduce a second thermocouple inside the furnace and to fix it as close as possible from the sample. If the sample is a bulk sample:Drill a hole inside the sample and put the thermocouple inside the hole and if the the sample is made of powder put it inside the powder. The are some miniature thermocouple (0.25-0.5mm diameter), mineral insulated which are unlikely to react with the samples. Patrick - Message d'origine De : Payzant, E. Andrew payza...@ornl.gov À : Mikko Heikkilä mikko.j.heikk...@helsinki.fi Cc : Rietveld list rietveld_l@ill.fr Envoyé le : Mer 14 Octobre 2009, 16 h 39 min 58 s Objet : Re: HT XRD calibration All, The two calibration standard method was described by Andy Drews (Ford Research Lab) in Advances in X-ray Analysis (the proceedings of the Denver X-ray Conference), vol. 44, page 44 (2001). Scott Misture (Alfred Univ), Stephen Skinner (Imperial College), Christian Resch (Anton Paar), and I ran a workshop on non-ambient diffraction at the Denver X-ray Conference in 2008, where we discussed many of these issues. There was a lively discussion with the attendees regarding various experiences with HTXRD, and the difficulty in abtaining the right answer. Too often we are so focused on the precision and accuracy of our refinements that we neglect the temperature issue, to our peril. One issue with the HT16 hot stage is that you will likely need to recalibrate with every new heater strip - don't rely on them behaving the same. Even for a particular strip, use of an internal standard is best if you can use one that does not react with either the strip or the sample. If you push this furnace to temperatures above 1200degC or so, the platinum will creep and the tensioning will change, so that the height/temperature calibration may subsequently be off. I agree fully with the suggestion to use parallel beam optics to eliminate the sample height error. You do lose some angular resolution of course, at least on a laboratory diffractometer, but you take one variable (sample height) out of the refinement. The other BIG problem with the HT16 (and many other non-ambient stages) is knowing the temperature of the SAMPLE (as opposed to the strip). Powders have hopelessly poor thermal conductivity, and the gradients in these furnaces can be substantial. We rarely measure the temperature of the sample directly, and this is another reason why internal standards are very useful - you can use either a known CTE to estimate the delta T over the full temperature range, or a known phase transformation to determine delta T at a single point. I personally prefer the former approach myself. Note that a solid-solid transformation may give a different result than a melting point standard, since the liquid will change the thermal conductivity between the strip and the sample. You can find more discussion of these issues in Mark Rodriguez's chapter in the book Industrial Applications of X-ray Diffraction, or mine in Principles and Applications of Powder Diffraction. I chair the non-ambient diffraction subcommittee of the ICDD, and in that capacity I am looking for ways we can develop and standardize these methods. If any of you would like to participate in this exercise please let me know. Perhaps a special issue of Powder Diffraction could be devoted to in-situ high-temperature diffraction papers? Always looking for good ideas... Andrew On 10/8
