Aluminum oxide isoelectric point

Silicon, titanium, chromium, and aluminum oxides should be relatively acidic, with isoelectric points near 4.0, 6.0, 7.0, and 7.0, respectively. Iron oxide should be intermediate, with an isoelectric point near 9.0. Parks predicted the isoelectric point of nickel oxide to be of the order of 10-12. Other investigators [20] have reported the isoelectric point of nickel oxide to be near 9.4. 

As indicated above, Mason et al. [13] found that the pretreatment affected the surface acidity of Ti-6,4. They found that surfaces treated with a basic etchant had an isoelectric point between 7.3 and 9.2. A phosphate-fluoride etch left the surface acidic with an isoelectric point between 5.4 and 7.3. As noted above, Finlayson and Shah [12] also found that the pretreatment affected the acidity of oxidized aluminum surfaces. 

Ermakova, L.E., Sidorova, M.P., and Smirnov, V.M., Isoelectric point of silicon oxide particles coated by monolayers of oxides of titaninm and aluminum. Colloid J., 59, 523, 1997. 

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