Aggregation of air-dry alumina powder nanoparticles redispersed in an aqueous medium

The aggregation of air-dry Al2O3 nanopowders prepared by electrical wire explosion (EWE) and plasma deposition in a gas atmosphere was studied by dynamic laser light scattering during redispersion in water. The specific surface of nanopowders was from 9 to 38 m2/g. It was shown that aqueous suspensions of nanopowders stabilized by a double electric layer with an electrokinetic ξ-potential magnitude of 30–40 mV contain coexisting individual particles and their primary aggregates (35–50 wt %). The average size of the primary aggregate is approximately three times larger than the average size of an individual particle. The former probably consists of a central particle surrounded by the first coordination sphere. As the medium pH varies from 2.5 to 11.5, the electrokinetic potential of the Al2O3 nanoparticle suspension monotonically decreases from +40 to −40 mV. Near the isoelectric point (IEP), aggregation is significantly enhanced, which results in the formation of larger secondary aggregates of 103–104 individual particles. The use of Na citrate as an electrostatic stabilizer prevents the formation such large aggregates, and only an increase in the fraction of primary aggregates and a decrease in the number of individual particles occur near the IEP.