Hello. I am dealing with sodium and lithium compounds, however it seems that a lot of sodium/lithium is evaporating during annealing process.
Can you share your experience, how do you deal with this problem?
So far I concluded that I obtain better results if the pelletized sample is covered by loose powders or even "submerged" in them.
Hi
You can wrap up the pelletized sample by aluminum foil, then you can annealed the wrapped up sample in a vacuum furnace.
To Dr. Habib. If you wrap a pellet by aluminium foil, you will receive:
1. Thin and brittle layer of lithium (or sodium) aluminate around the sample; 2. A tablet enriched on the surface with aluminium. This is not the result that is needed.
To Mr. Nowak. Method you used (pellet under covering), is best of known in SSCh. All you need in addition is to determine the excess of lithium or sodium (in oxide form). This amount depends on synthesis conditions, pellet shape, density etc. That is, you must repeat these parameters during several subsequent attempts of synthesis.
Therefore, you will synthesize, under the same conditions, several samples with an excess of the volatile element. (For example: 0, +2, +4%). After that, make the XRD spectra and build the dependencies of relative intensity of any impurity reflex vs. the concentration of excess element. By extrapolation, you find the desired concentration of excess. If you perform a synthesis with this excess value obtained by same way under same conditions, you will get an almost pure phase of the substance required.
Regards.
The actual composition of the Al foil surface is supposed to be made of Al2O3 rather than a pure Al. The Al2O3 film has not only good heat resistance but also a chemically passive film. This is the reason behind Al foil as a good wrap materials at high temperature.
The vapors of lithium and sodium oxides (like all alkali metals) react very actively with most oxides and metals (even with platinum, I have seen it, unfortunately). Especially since no wrapping will be gastight. Therefore, wrapping is not suitable (maybe synthesis in a sealed cell (what material? – it is gold!) can be done, but it is quite difficult technically as well as very expensive).
We are talking, of course, about high temperature conditions. However, if alkali loss observed, then these are high temperatures. Losses are intensified in the presence of water vapor (hydroxides are more volatile than oxides), i.e. when he synthesize in air or use hydroxides as a starting material.
The calculated excess can compensate the losses; I briefly showed how to do it.
So, the question now is for Makolaj, what is the temperature range and atmosphere of annealing conditions.& as Daniela has raised already such a question.
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