Nanoparticles of Barium Ferrite Synthesised Using a Water-in-Oil Microemulsion

The application of barium ferrite (BaFe12O19 ; BaF) in the magnetic media industry requires materials with strict control of homogeneity, morphology and magnetic properties resulting from their preparation and pretreatment. Here the use of water-in-oil microemulsions for the synthesis of nanoparticles of BaF is considered. Two microemulsions (containing an aqueous phase, cetyltrimethylammonium bromide surfactant, n-butanol co-surfactant and octane) were used. The aqueous phase of the first microemulsion contained ferric/barium salts and the second co-precipitant ammonium carbonate. On mixing, the aqueous cores acted as microreactors for co-precipitation of the BaF precursor which was then separated, dried and annealed (1198K, 24h) to form BaF. It is shown that microemulsions prepared with different surfactant concentrations lead to particles with variable but controlled morphology and magnetic properties. In particular, it is shown that selecting a microemulsion with a specific concentration can allow coercivity and particle size of product to be nano-engineered

Catalysis by well characterized materials - discussion

General discussion: Prof. R. A. van Santen (University of Technology, Eindhoven, The Netherlands commented: I would like to point out that the predicted reactivity of bridging 0 species agrees with the results of Pauling's valency rules. I would like, to ask whether it would not be better to study clusters containing Mo as well as V, since the acidic proton coordinated to the bridging oxygen is generated by vanadium. If one were to apply thermodynamic arguments, which of the oxygens (bridging or monocoordinated) would be most active