Dear viewers,
I am working on ball milling of Aluminum powders for a couple of years and a question yet not answered to me is that "why sometimes- not always or so many- I encounter a color change in my yield after ball milling?" As we all know the color of Aluminum and its oxide, for that matter, is somewhat grey but why sometimes it changes into black or dark grey. I considered the burning of powders and also the impurities as the reason but when all the parameters are the same is there a possibility of happening on and off??
Thanks in advance for the answers you share.
When you process a powder, you may induce various phases of aluminum oxide (different crystal structures). The presence of multiple oxidation states often results in absorbance in the visual light spectrum broadening, taking standard colors and darkening them. (Example: Manganese oxide in 2+ oxidation state is green, +3/+4 is brown, and a mixture of all of these is usually black.) Careful processing and annealing can often help in tailoring your properties. Best of luck with experiments!
When you process a powder, you may induce various phases of aluminum oxide (different crystal structures). The presence of multiple oxidation states often results in absorbance in the visual light spectrum broadening, taking standard colors and darkening them. (Example: Manganese oxide in 2+ oxidation state is green, +3/+4 is brown, and a mixture of all of these is usually black.) Careful processing and annealing can often help in tailoring your properties. Best of luck with experiments!
Some times this may happen with the prevailing conditions of processing like humidity, salts and gases present, acidic environment
Ball milling increases the surface area and your material becomes more prone to reaction with the surrounding (e.g., oxygen, moisture, and even balls).
Aluminium is very easy to oxidize and decreasing particle size will increase the surface area and the oxidation accordingly. In addition this behaviour can become a lot worse depending on the alloy composition (such as Mg content in Al).
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