Hello! I am trying to synthesize a MAX phase powder using the molten salt method. For the heat treatment of the powder, someone advised our group to anneal our samples in pellet form rather than putting it as is in a crucible. Is there an advantage in annealing the sample in pellet form?
Dear Raniella,
The advantages in annealing in pellet form are as follows:
1. Your material is in a compact form and thus the atoms that have to travel to make it homogeneous is close by.
2. If there is some melting of the sample, it will not lead to inhomogeneity.
3. If there is some phase that can possibly evaporate, the compacted pellet will reduce it's chances due to lesser surface area being exposed.
Hope these help you.
~Anirudha~
Dear Raniella,
At synthesis in molten salts the formation of the solid phase occurs at a sufficiently high temperature where diffusion processes cause a high rate of crystal growth. The main problem is to eliminate adverse capture of side component compounds by synthesized powder. On the surface of powders, since a surface area is greater, contaminants (water, oxygen, carbon dioxide, etc.) are adsorbed considerably more than when using pellets. Therefore, it is more reasonable to use pellets.
Sincerely,
Svetlana V. Chuppina
Thank you so much for your answers.
Will this affect the melting of the salt? Will it retain the pellet form during heat treatment? I am sorry for asking such questions. It is my first time to do this experiment and I just can't visualize/imagine what will happen during the heat trwatment.
Dear Raniella,
If the entire salt mets then you will not get it in pellet form after the experiment. However, if a thin layer of oxide is formed on the surface it will prevent the melting of the compound totally.
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