Dear Bhoopesch, a typical design for a liquid sample cell is shown in the 2006 HASYLAB annual report, p. 76 (E. Welter et al.): http://hasyweb.desy.de/science/annual_reports/2006_report/part1/contrib/25/1... The cell consists of teflon spacers with stainless steel plates on both ends. These plates hold some kind of X-ray transparent window in place. A syringe can be used for filling and emptying the cell. Now, for your special application, the choice of the window is critical. However, at 10 keV you are not really limited to special materials like Be or BN, with ultralow scattering cross sections. The absorption length of a typical carbon-based polymer at 10 keV is already around 0.2 cm, which means that you could just use a regular polyethylene vessel with 1 mm wall thickness as "sample cell". I wouldn't use Beryllium, due to several reasons. With organomercury compounds, the chemical stability of Be could be an issue. I could imagine the formation of Beryllium amalgames, which are unstable in air and decompose to powders, as in JACS 1957, 3925. Also, Be windows are an inherent safety issue and should be avoided whereever possible. Have you investigated the applicability of Teflon-coated Kapton foil, like the FN type of DuPont ? We've used this type of foil (150FN019, teflon side towards the reaction cell) as window for many different reative gas atmospheres, like ammonia, acrolein, CO/CO2,... at elevated temperatures and never had problems with chemical stability or permeability of these foils. You could for example use some thicker variants like the 250FN029, with 50µm Polyimide / 13µm Teflon, or the 400FN022. Best regards, dominik Bhoopesh Mishra wrote:
Dear All, I am planning to conduct an EXAFS experiment which involves dealing with methyl mercury. Obviously, I want to be as cautious as I can in sealing the sample. In that connection, I am wondering if anyone on this forum can advise me regarding the best way to have a completely sealed (air tight) sample holder. My requirements are given below. Third requirement is not as important as the first two.
1. Sample cell (or the front and rear exit) should be made of low scattering material that would not attenuate photons too much at ~ 10-12 keV. 2. The sample cell should be a perfectly sealed, as gaseous phase methyl mercury or even di-methyl mercury could be produced in the cell. 3. I would like to inject solution using syringe in the sealed sample holder (if possible, this requirement is not necessary).
Among several possibilities, I am thinking of designing a cuvette shaped rectangular box with a thin bottom section, and probably using some sort of polypropylene such that scattering is as low as possible. It should be easy to put two silicon rubber septa on the top.
Other possibility could be using a thick Beryllium window (and please forgive my naivete' here - isn't there some restriction in using Be) on both the front and back of a rectangular or cylindrical box with rubber stopper at the top.
The easiest and probably the best would be to have a commercially available sample cell that can serve my purpose. I don't know any commercially available product like that. But I suspect, people who work with volatile material and/or radioactive material might know a lot about it.
If you know anything, please write me back. Any comments, suggestions, or criticism would be highly appreciated.
PS: Sealing with kapton tape (or any other thin film) might not be enough in this case as gaseous phase methyl mercury might diffuse through kapton, and also air might diffuse through kapton making the inside of the cell environment aerobic while I need to do this experiment anaerobically.
Thanks for your help! Bhoopesh
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