Comparison in the coating of Mg(OH)2 on micron-Sized and nanometer-Sized Nb2O5 particles

Abstract

Using Mg(OH)2 coating on Nb2O5 particles as a model system, the effects of core particle size and that of aging on coating in an aqueous environment were investigated. Specifically, two Nb2O5 particle sizes were used in this study: micron-sized commercial Nb2O5 powder and 17-nm synthesized Nb2O5 particles. Coating of Mg(OH)2 on Nb2O5 was carried out by precipitating Mg(OH)2 from magnesium nitrate in an aqueous Nb2O5 suspension. The coating behavior of Mg(OH)2 on Nb2O5 was examined with optical microscopy, zeta-potential measurement, and local chemical analysis by energy dispersion spectroscopy (EDS). The results showed that the size of Nb2O5 plays an important role in the coating behavior of Mg(OH)2. Optical micrographs, zeta-potential measurements, as well as local EDS analysis all indicated that coating Mg(OH)2 on micron-sized Nb2O 5 particles was easier than on nanometer-sized Nb 2O5 particles. We attribute the difficulty in coating Mg(OH)2 on nanometer-sized Nb2O 5 to the enhanced dissolution of Mg(OH)2 by the nanometer particle size as a result of the Kelvin effect. Aging improved the coating on micron-sized Nb2O5 but did not exhibit significant improvement in the Mg(OH)2 coating on nanometer-sized Nb2O5 particles. It is likely that aging modified the coating behavior of Mg(OH)2 on Nb 2O5 via a dissolution-re-precipitation mechanism.