my work includes mechanical milling of aluminum powder in argon environment and methanol as process control agent. If aluminum powder has already interacted the atmosphere during taking samples and other work etc, then what are the effects of ball milling on oxygen layer developed on powder. Is it converted to alumina or aluminum can be restored in ball milling.
The reaction 4Al + 3O2 = 2Al2O3 runs in only one direction: the formation of alumina. The longer and more active the milling, the larger is the Al2O3 content in the finished powder. Argon and methanol help only a little: aluminum pulls the oxigen also from methanol.
No matter what you do, in fine aluminum powder is more than 30% of Al2O3.
The effect of ball milling will be to continually break up the oxide layer that forms on the surface of the powders and distribute it in the powder. The result will be an oxide dispersion strengthened aluminum. Methanol as a process control agent has some drawback in that there is some solubility for water and this will help form the oxide.
hey thankz.. i have done milling for three hours at different graphene percentages. Different variables are:
100 gram aluminum powder with different graphene reinforcement(0.5 wt %,0.75 &1 wt %), BPR is 4.7, vial is of 500 ml capacity, milling done in argon environment, milling times 3 hours, Process control agent 1.5 wt %of Aluminum powder which is 1.5 ml (methanol).
after completing 3 hours once i opened vials i observed powder sticking to vial bottom and a small amount of powder and balls were free to rotate. i had to scratch off the milled powder which however was easy but it seems to be not moving once milling in operation. for reference i have attached one image also. moreover few traces of un-dispersed graphene were also observed.
Im looking for the answer why powder sticking to bottom and not moving with vial movement. Also milling machine is a planetary ball mill
Increase BPR to at least 10 to 1. Balls should be the same size. Use just enough PCA to cover the powder and balls in the vial. Please see attached papers for some specifics on the MA of aluminum alloys.
Article The effect of mechanical alloying on SiC distribution and th...
Article Mechanical alloying to produce L1(2) phases in the Al-Zr system
Article Synthesis and properties of trialuminides with ultra-fine mi...
Article Formation of metastable L12 phases in Al3Zr and Al-12.5%X-25...
About possible corrosion of aluminium by anhydrous alcohols:
Anhydrous methanol ― and also ethanol, n-propanol, and isopropyl alcohol ― may possibly react with the Al particles, particularly if heated to facilitate particles drying after milling. To avoid possibly extensive reaction with Al particles, the mentioned alcohols should not be used hot and should contain at least around 0.2 wt% H2O. To avoid or limit corrosion of Al particles, it may be convenient to ensure, say, around 2 wt% H2O. Below about 0.2 wt% H2O, the reaction of such relatively low molecular weight alcohols with powdered Al can become quite vigorous at the normal boiling temperature. Al corrosion by the mentioned anhydrous alcohols can be expected to increase with the particle's specific surface area, temperature, and contact time; and to decrease with water content ― except if quite high; say, above 20 wt% H2O ― and with the molecular weight of the alcohol. Butyl alcohol, as other higher molecular weight alcohols, would be not expected to react with Al, even if dry or heated.
After noticing ― from a post issued above by the question's author ― that aluminium should be milled and homogenized with added graphene for reinforcement (0.5 to 1 wt%), I think that good wetting and compliance with the relatively high hydrophobicity of graphene can be achieved by selecting either butyl acetate or liquid paraffin as process control agent (PCA).
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