I am doing UHV thermal evaporation of Calcium metal from calcium metal grenules. For powdered oxides we use a cover having holes in it above the boat. Should I use same for calcium?
No. any material used as covering may introduce as contamination unless the covering itself is the same material as the evaporating material. If your concern is about the "boiling" off the boat, just pack it dense for thermal contact and heat it with gradual increment.
Hi mangal,
cover with holes is of the same metal as of boat, so should not give contamination. and please elaborate what is boiling off and what to pack densely for thermal contact. Although I heat it gradually.
I also saw some ash left in boat rather than accumulated ball of metal.
It depends on the evaporating temperature. I used to see the Mo or W on the thin film (when I evaporate Ag, Au, Cu, Ti) from RBS, PIXE spectra whenever I used Mo or W boat. The species concentration were miniscule but the respective contamination were detected. So, if the minimal contamination is not the issue, it is safe to practice your way. The rule of thumb is the evaporating temp should not exceed 33% (1/3) of its' melting temp. So, the melting temp of Ca, Mo, W are 842, 2623, and 3422 degree C respectively, I think it is safe to do so with the risk of minimal contamination from boat material.
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