Aluminum oxide dissolves in alkali. Nanoparticles react better, than large particles

Al2O3 + 2NaOH + 3H2O = 2Na [Al (OH) 4]

The sodium silicate hydralizes to form an ion hydroxide that will react with aluminum oxide

SiO3 2- +H2O =H2SiO3 +OH-

Al2O3 + 2OH- = ...

Dear Yuri Mirgorod

Thank you for your answer.

Actually, I tried to dissolve nano-alumina in 10M NaOH solution. It could not be dissolved and every time I found it as sediment.

I tried to add in liquid sodium silicate, it might reacted. because sodium silicate became very sticky (viscous).

In both case, the ambient temperature was about 30 degree celsius.

Thank you.

Are you sure that the alumina nano-particles are not containing surface impurities?

Or, in other words, please give some info on your nano-alumina:

- is it a powder or a thin film?

- how was it obtained and

- which were the characterization analyses you did on it

- with what results?

otherwise is like shooting in the dark... and any answer can be as good or as bad as the other...

Consult with prof. Anca Duta/ She asked you correctly.

Dear Professor Anca Duta

Thank you. We bought nano-Al2O3 through supplier.

It is powder form.

I will do the XRF and XRD tests. Do you have any other suggestion for characterization and checking if any surface impurity?

Thank you.

I would suggest an EDX (EDS) analysis to get the surface composition of the powder grains.

If EDX is not available the following can be tried:

- Overall, Al2O3 is amphoteric and therefore it would react with, e.g. HCl.

- So, try to insert a few powder grains in HCl (1...2 mol/L) to check if there is any reaction. The grain are expected to react and the resulted chloride(s) are water soluble for the large majority of cations.

- If this happens, then analyse the solution, looking for different other cations (other than Al).

- If not, try a different analysis (e.g. XRD) to find out what the powder really is. However, be aware that XRD will give relevant results if the nano-powder is crystalline. So, XRD can be in the situation of not giving the expected answer to the question "is it Al2O3 or not?"