  The agglomeration, electrokinetic properties and electrophoretic deposition
behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were
studied in comparison with conventional pH adjustment. It was found that citric
acid imparted negative zeta-potential values and electrosteric stabilisation to
particles in suspensions at all pH levels. The examination of additions of
carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp
drop in zeta-potential at distinct addition levels, which correspond to surface
saturation of the particles with negatively charged carboxylate groups.
Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated
from these results, showing that both citric acid and EDTA coordinate to ZrO2
surfaces by two carboxylate groups while oxalic acid is coordinated by one
group. The use of carboxylic acids was shown to facilitate superior
electrophoretic deposition in comparison with zeta-potential modification by
conventional pH adjustment through improved suspension stability.
