Recently I have been trying to make Mn-containing alloys by using vacuum arc-melting furnace from pure metals.
However, when we check the surface of the specimens cut from the as-cast button, we found that there are many MnOx particles inside of them.
Even I removed the oxidation layer of pure Mn immediately before the experiment, there are still many particles.
Does anyone have ideas to avoid this kind of MnOx particle?
Any small techniques will be appreciated.
Mn oxidizes very quickly. How did you remove the oxides before arc melting? The best solution is to have a furnace which you can run under hydrogene and under vacuum as well. In this case you can remove the oxygen and you can start arc melting without fresh oxidization. in between.
As already said, you have to pump and purge the inner atmosphere of your arc furnace with pure Ar. Your problem comes from a too high residual oxygen pressure in the reactor.
Then, you can perform a first run on some metal getters like Zr before melting your Mn samples.
Thank both of you for providing me your ideas.
Actually, in my case, arc-melting is performed under protective pure Ar atmosphere, and pure Ti fragments were used as an oxygen getter. Before melting, the oxidation layer of Mn is removed by diluted nitric acid solution.
Using hydrogen would be one of the solutions, but I think there is a safety problem.
The evaporated Mn becomes fine powder accumulating in the furnace, and I am afraid that the mixture of the powder and hydrogen gas could cause dust explosion.
A dust explosion would only occur in the presence of oxygen. Using plein hydrogen in a closed chamber is safe. In case of floating hydrogene you need in any case an eternal flame to burn the leaving hydrogene.
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