Recently I started to use XRD to study the structure of some molecular sieves. My powder sample was prepared by grinding in a mortar, drying in an oven, and loading on the sample holder. However, I was told I missed one procedure, that is before loading on the sample holder, the dried sample should be placed in a sealde container together with a glass of saturated Calcium chloride (CaCl2) aqueous solution. I don't understand the purpose of this very operation, and I don't even know if it's right. Can any experienced researchers help me to figure it out? And what is the standard preparation procedures of PXRD sample?
Dear Chenhao Wei , I agree you, I don´t understand the purpose of this operation. CaCl2 is a dissicant, but you already has your powder dried/calcinated in an oven. this operation could have some sense as a way to store the samples if they have to wait for a long time before the XRD measure. Using a saturated aqueous solution of CaCl2 is even more strange. I was checking if it could be used for some kind of ion exhange with your molecular sieves, but since they are not in contact, such exchange is not possible.
Placing your molecular sieve powder inside a sealed container together with a glass of aqueous saturated CaCl2 would probably cause hydratation of that powder, since -often- molecular sieves are better dissicants and able to remove water molecules from the air inside the container. If the pourpose of the operation would be that of studying differences between the hydrated and dehydrated molecular sieve, it would be enough to place a glass of water inside the container.
Dear Chenhao Wei , I totally agree with Manuel Gómez . Though I would like to point a few additional points that moisture has a role in this procedure. As we all know that CaCl2 assists by absorbing water vapor from molecular sieves since they are fast-drying agent having the ability to trap moisture. By this process, we can negate the error in PXRD due to the presence of moisture in the sample. For more insights, I would request you to go through Article Crystallization and Catalytic Properties of Molecular Sieve ...
Manuel Gómez Kaushick Parui Thank you for your detailed answers! Nibou Djamel And thank you for your comment!
Respected sir,
Your process looks good and perfect. But please check that your sample is hydrophilic or not. If yes then you have take some precautionary steps before putting it in XRD. Hope my answer will help you for the further process.Thank you.
I think your powder has many H ions you must exchang them with CL ions. It will help your powder don't form hydrogen bond
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