Spherical particles and their surface properties

Abstract

Spherical particles of transition metal oxides (vanadium oxide, manganese oxide and iron oxide) were formed by the use of O₂-H₂ flame fusion and the effect of varying raw material on the product particles was investigated. Particles ranging in size from 50 to 0.01 μm were produced simultaneously by explosive decomposition of raw material which is composed of higher valent metal ions, and melting to give V₂O₅ → V₂O₄ +$\tfrac{1}{2}$O₂; Mn₂O₃ → 2MnO +$\tfrac{1}{2}$O₂; and 3Fe₂O₃ → 2Fe₃O₄ +$\tfrac{1}{2}$O₂. During cooling from the molten state particles were reoxidized completely or partially (in the surface layer) into V₂O₅, Mn₃O₄ and Fe₂O₃, respectively, depending upon the particle size. A cavity was observed electron microscopically in the smaller V₂O₅ particles, while fine single crystal (exactly polyhedral but almost spherical) particles of Mn₃O₄ and Fe₃O₄ were obtained. The isoelectric points of spherical Mn₃O₄, Fe₃O₄ and Fe₂O₃ particles were determined to be 4.0, 5.1 and 5.1, respectively.