Hi!
In our institue we are using following mixture:
4.8 g K2Cr2O7
20 g 50% H3PO4
fill up to 100 mL with destilled water.
We found it4s the best recipe to remove the alumina. (ca. 70-800C)
Nearly all chromic  compounds are carcinogen. But don`t be afraid,
if you pay regard to some safety regulations, it`s no problem.




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Dipl.-Chem. Matthias Kruse
Institut fuer Anorganische Chemie
Fachbereich 8
Universitaet Essen
Universitaetsstr. 5-7
45117 Essen

Tel.  +49 (0)201 183-4515
Fax.  +49 (0)201 183-4195
email matthias.kruse@uni-essen.de
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