Dear Fathie,

I think short-time low-energy milling using Al2O3 balls and PE bottle does not have a negative effect on your powder.

It depends what you consider to be a negative effect. If pulverizing it into a very fine power is a negative effect then yes.

1 Impurities from balls will enter to your powder if the milling time is too long.

2 After milling for a critical time, depending on your equipment, the particel size will not decrease.

Is number 2 a negative effect?

If you consider a partial amorphization of alumina due to milling is a negative effect then yes. However amorphization will also depends on milling efficiency, ball to powder ratio, mill load etc. You just need to decide it by yourself.

That was not what number 2 said. In any case I cannot imagine ball milling alumina could cause amorphization (at least during my life span). It can't even produce nano scale particle sizes. Amorphous alumina produced by ball milling? Not possible unless the ball milling machine is heated to 3000 C and then quenched to room temperature in a milliseconds.

There was no mention about nan-sized alumina. It is very clear that alumina will again re-agglomerate when particle size reduce below 200 nm. I said a partial amorphization and that occurs even you use a ball mill. About your life span I am not sure. But there are a several papers by Ban and Okada where you can find mechanochemical effect on milled Alumina powders. Journal of Materials Science Letters

1 June 1993, Volume 12, Issue 11, pp 862-864

Mechanochemical effect for some Al2O3 powders by attrition milling

K. Okada, A. Kuriki, S. Hayashi, T. Yano, N. Otsuka

I mean removing of coupling agent layer.

Thanks.

It is better that you dry the powders at lower temperature to avoid agglomeration. Then long time milling is not necessary.

Could you please suggest a temperature? I use 80C.

Dear Fathie,

Maybe you can break the agglomeration (after drying process) in short time by using these parameters: Type: dry milling / Time: one minute / speed: 150 rpm...OR just do it manually by using ceramic mortar bowl & pestle....THEN, you can use (TEM) to characterize your treated powder.

Thanks.

Dear Fathie,

It is not clear what do you call "negative effect". It depends on the further application of alumina.

If the only goal is the preparation of fine active alumina powder, milling in a ceramic ball mill (may be with some water) is the best process to avoid the effects of aggregation and mechanical activation. The last phenomena are atributable to planetary mills and shakers.

If you supposed to use alumina as reagent, the mechanical activation can be usefull. Please, see the paper 

Andryushkova O.V., Ushakov V.A., Kirichenko O.A. and Poluboyarov V.A. Effect of mechanical activation on phase transformations in transition aluminas. Solid State Ionics, 101-103 (1997) 647-65335.

and other papers of that author in 1990-2000. I am afraid, I dont have its copy