Jools, You are right. “Lab grade” bottled N2 may have enough residual oxygen to cause problems, plus it is hard to purge the chamber properly to get the pO2 low enough to avoid issues. But an H2/N2 mix might not be suitable, especially if it destabilizes his sample. Here are some other ideas:
1. I used to flow high purity N2 through a gettering furnace in series with the HTXRD chamber, and that, coupled with multiple purges of the chamber prior to starting the experiment, worked pretty well. 2. I have in the past used a Bühler HT furnace that had a secondary “surround heater” option. I had some success putting a gettering wire across these leads and running it at a higher temperature than the heater strip in order to remove traces of oxygen from the chamber. This has the advantage that as you heat up the walls of the chamber and release adsorbed oxygen it goes to the getter rather than the strip. It can be a bit tricky ensuring that the getter is hotter than the strip across the range of temperatures that you run. However, I fully agree with you that a platinum foil is probably a better option for Blaise’s experiment. If he has one handy. There are some caveats regarding platinum though. It is generally more expensive. It is readily attacked by silicon, iron, and other elements. You can get recrystallization and/or rapid grain growth at high temperatures, which dramatically changes the diffraction pattern from the strip during a HTXRD experiment. The relatively high CTE means that the strip height will change as the temperature increases, which will cause large peak shifts unless you are using parallel beam optics and even then will cause intensity variations at the lower 2thetas. If you work at a US government lab, platinum is a precious metal and there is some paperwork required every time you change heater strips. Also, if your sample melts or sinters, you may have some “fun” getting the platinum clean. Andrew ***************************************************** Dr. E. Andrew Payzant Materials Engineering Group Leader Neutron Scattering Division Neutron Sciences Directorate Mailing address: Oak Ridge National Laboratory Dr. E. Andrew Payzant P.O. Box 2008 Bldg. 8600, MS 6475 Oak Ridge, TN 37831 cell: (865) 235-4981 email: payza...@ornl.gov https://www.ornl.gov/staff-profile/e-andrew-payzant ****************************************************** From: Julian Richard Tolchard <julianrichard.tolch...@sintef.no> Date: Thursday, July 25, 2019 at 10:47 AM To: "Mibeck, Blaise" <bmib...@undeerc.org>, Andrew Payzant <payza...@ornl.gov> Cc: Rietveld list <rietveld_l@ill.fr> Subject: RE: [EXTERNAL] Mounting Sample on High Temperature XRD Ribbon Heater Actually, i wouldn't recommend that either 😊 My experience with the Ta heaters is that they react with even the smallest amount of oxygen, and bottled N2 has more than enough to kill a Ta strip. The best result we had was with a H2/N2 mix, but that still failed (probably reaction with the sample). Personally I think the only reliable way to use them is with a high vacuum system (turbo pump), and with relatively inert samples. Ultimately you are better off getting a Pt strip instead. Jools From: rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> On Behalf Of Mibeck, Blaise Sent: torsdag 25. juli 2019 16.27 To: Payzant, Andrew <payza...@ornl.gov> Cc: rietveld_l@ill.fr Subject: Re: [EXTERNAL] Mounting Sample on High Temperature XRD Ribbon Heater Thank you -- I will try nitrogen then! ________________________________ From: Payzant, Andrew <payza...@ornl.gov<mailto:payza...@ornl.gov>> Sent: Thursday, July 25, 2019 9:08 AM To: Mibeck, Blaise <bmib...@undeerc.org<mailto:bmib...@undeerc.org>> Cc: rietveld_l@ill.fr<mailto:rietveld_l@ill.fr> <rietveld_l@ill.fr<mailto:rietveld_l@ill.fr>> Subject: Re: [EXTERNAL] Mounting Sample on High Temperature XRD Ribbon Heater STOP!!! The tantalum foil should not be used for high temperature in air. Above a few hundred degrees Celsius it will oxidize rapidly and disintegrate. I accidently learned this the hard way many years ago! 😉 Either use an inert atmosphere or vacuum. Or use a different heater ribbon, suitable for air atmosphere. Andrew ***************************************************** Dr. E. Andrew Payzant Materials Engineering Group Leader Neutron Scattering Division Neutron Sciences Directorate Mailing address: Oak Ridge National Laboratory Dr. E. Andrew Payzant P.O. Box 2008 Bldg. 8600, MS 6475 Oak Ridge, TN 37831 cell: (865) 235-4981 email: payza...@ornl.gov<mailto:payza...@ornl.gov> https://www.ornl.gov/staff-profile/e-andrew-payzant ****************************************************** From: <rietveld_l-requ...@ill.fr<mailto:rietveld_l-requ...@ill.fr>> on behalf of "Mibeck, Blaise" <bmib...@undeerc.org<mailto:bmib...@undeerc.org>> Reply-To: "Mibeck, Blaise" <bmib...@undeerc.org<mailto:bmib...@undeerc.org>> Date: Thursday, July 25, 2019 at 10:03 AM To: Rietveld list <rietveld_l@ill.fr<mailto:rietveld_l@ill.fr>> Subject: [EXTERNAL] Mounting Sample on High Temperature XRD Ribbon Heater I am looking for advice on how to prepar a HTXRD sample (mounting techniques, stage preparation, etc...). The ribbon heater is tantalum (brand new). The sample contained ammonium di-hydrogen phosphate. The atmosphere is air. I hope to reach at least 1100C, but have had the ribbon break before 750C. Corrosion? or can the sample lower electrical resistance? Please, any advice. All the best, Blaise
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