Aluminum Powder and PM Technique

Are you dealing with Aluminum metal (Al) or Alumina (Al2O3) powder?

Can you tell me where you are located?

Is the process used to make aluminum powder is based on sulfuric acid based disslution.

If this is true then in presence of iron contamination which is common in high purity alumina to have PPM level and that is enough to produce some H2S gas and that may be what you are seeing. This smell should be gone after few minutes holding at elevated temperature.

Do you see this.

Hi,

the oxide layer is not really thick except if powder fabrication was bad.

If we cut a fresh aluminum surface in lab atmosphere without cooling at near room temperature then there is no layer for some hours and after 24 hours around 10 nanometer layer.

If powder is made from sprayed molten Al then there may be anything fro totally burnt to nearly no layer. This is largely depending on the oxygen and water content of the vacuum or inert gas into which is sprayed.

These layers - if oxide only - are usually not compact oxides but have (nanometer size) pores where water is absorbed and then is reacted to Al-oxide-hydroxide and the residual pores absorb anything existing, mainly water.

(We measured outgassing behaviour for vacuum purposes, you will see anything but mainly water in considerable quantities.)

Considering your bad smell at heating this is mostly reaction of trace contaminants in the Al with oil, fat, other organics and proteins.

This can give bad smell with incredibly low amounts - try with lead containing brass on touching with fingers - the smell will be on your fingers but any forensic lab will have big difficulties to analyse and estimate what it is and how much. I don't think it is H2S.

Try to order different batches of the Al powder (purity 10-4 and 10-5?) to be made in inert gas with 20, 7, 2.5 ppm oxygen (as water plus oxygen) in nitrogen or else. And try if you find a limit where the effect is vanishing.

If I am hand grinding our chrome steel kitchen knives on waterproof SiC-grinding-paper then I have a similar bad smell. This is a reaction product of the phenolic binder of the grinding-paper and the metals.

To avoid maybe harmful side-effects: get an active carbon filter to absorb and check how often to regenerate!

RHABE

I agree 100 percent with you. I remember my days of making aluminum metal paste and some time when we heated did had bad smell and tracing it back it was fatty acid which is used to make the paste had contamination of the alumina.

Fatty acid is made using other solvent and organics to make hot melt paste of aluminum for solar application. This was also true when we made thick film paste but this time comtamiantion was poor handling and the smell was human hand

Only one time I in my memory I was blaming alumnum manufacturer and finally settle down on sulpher and iron contamiantion theory and I may be wrong based on evidence I have of smelling from other sources

Thanks a lot for all of you