I'm looking for a simple recipe to coat particles of alumina (100 micrometers of diameter) with a silica layer (1 micrometer thick). I need to produce one kilogram of powder of alumina/silica coated particles. I thought about sol-gel procedures, but which one would be the best ? Are there other ways ?
Dear Dr. Polesel:
Really, the chemical synthesis is the most effective procedure to attain a coating of the alumina particle. The thickness (1 micrometer) of the shell is not exact, the further procedure seems an industrial "type aspect". The simple and best way seems to use of the classical Pechini method that is flexibe to molecule that countain de cation of interest as Si. It is possible that as Si source, an alkoxide can be used. Consider the alumina particle as being a sphere, derive the volume associated to the shell that is required. In the sequencie derive the mass SiO2. Derive the amount of Si in this oxide mass. Select a precursor that contain Si soluble in water or ethilene glycol, derive its amount necessary to entry with exact amount of Si in the synthesis. It is possible that some small portion of acid be necessary, since that the acid actuate during the polyesther formation (citric acid more ethylene glycol). Several compositions of polyesther are possible, but the classical relation is 60 wt% of citric acid and 40 wt% of ethylene glycol. Typically 3 mols of citric acid is used to each mol of to be complexed. Also, it is possible that Poliol-modified method can be used. There is a great number of paper in material preparation, some of them has been authored or co-authored by M. A. L. Nobre, see item publication.
I have only coated nanoparticles, but I am sure, the procedure is the same. I was following the procedure by Miachel Kacenka described in:
DOI: 10.1063/1.4867958
Article Magnetic properties of La1-xSrxMnO3 nanoparticles prepared i...
I think that you can do this with no difficulty. If you have SiCl4 or other compounds of Si (with SiH for example), make a dilute solution of it in suitable solvent (example toluene) add alumina with stirring, then add drops of water.
The Si compound will be converted into a gel coating on Alumina particles.
You may need to anneal the resulting system
Must be careful:
- Concentration control is important to make film very thin
- amount of alumina must be carefully chosen
- Stirring must be very fast
- Try to make the sol-gel reaction as slow as possible
- You will need to do the experiment many times to have the best working conditions and to control the resulting films of SiO2
Dear all,
Thank you very much for your suggestions, they are very helpful.
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