ABSTRACT
Bulk samples with high mechanical strength reaching 1000 MPa were obtained from electroexplosive Fe-Fe3O4 nanoparticles containing 81 wt. % Fe. Maximum strength is achieved by consolidation of the nanoparticles by isostatic pressing followed by vacuum sintering at 700 °C. A further increase in the sintering temperature leads to the formation of large pores with a size of up to 5 µm and an intense interaction of Fe and Fe3O4 with the formation of FeO leading to the embrittlement of the samples and a decrease in their strength. The degradation rate of Fe- Fe3O4 samples in NaCl (0.9% wt.) and Hank's solution is 7 times higher than that of samples obtained by sintering an electroexplosive Fe nanopowder under the same conditions.
ABSTRACT
A novel route for the synthesis of boehmite nanospheres with a hollow core and the shell composed of highly crumpled AlOOH nanosheets by oxidizing Al nanopowder in pure water under mild processing conditions is described. The stepwise events of Al transformation into boehmite are followed by monitoring the pH in the reaction medium. A mechanism of formation of hollow AlOOH nanospheres with a well-defined shape and crystallinity is proposed which includes the hydration of the Al oxide passivation layer, local corrosion of metallic Al accompanied by hydrogen evolution, the rupture of the protective layer, the dissolution of Al from the particle interior and the deposition of AlOOH nanosheets on the outer surface. In contrast to previously reported methods of boehmite nanoparticle synthesis, the proposed method is simple, and environmentally friendly and allows the generation of hydrogen gas as a by-product. Due to their high surface area and high, slit-shaped nanoporosity, the synthesized AlOOH nanostructures hold promise for the development of more effective catalysts, adsorbents, vaccines and drug carriers.
